You can turn some HP desktop power supplies into useful benchtop sources for fixed DC rails, but only after confirming the exact PSU and connector. HP models are not universally wired like standard ATX supplies: a verified ATX unit can usually be enabled with its active-low PS_ON# signal, while a proprietary HP unit needs its own documented pinout. The result is generally a fixed-voltage breakout supply, not an adjustable laboratory supply.
What this project makes—and what it does not
A basic conversion exposes the voltages already produced by the PSU at insulated terminals. Depending on the exact model, those may include +3.3 V, +5 V, +12 V and a low-current −12 V rail. It does not make those outputs adjustable or add current limiting simply by adding binding posts.
- Output breakout: Existing fixed rails are switched and brought to terminals.
- Protected breakout: Adds suitable output fuses, insulated terminals, a proper enclosure, labels and optionally meters or a minimum-load arrangement if the specific supply requires one.
- Adjustable output: Adds a suitable DC-DC converter after a PSU rail. The converter determines the output range and current-control behavior; the HP PSU remains the input source.
For sensitive or valuable electronics, a purpose-built bench supply is preferable when adjustable voltage, reliable current limiting, accurate metering or published ripple specifications matter.
Identify the exact HP PSU before wiring
Read the label on the supply and record the HP computer model, PSU model or spare-part number, rated wattage, input range and listed output rails. Inspect the connector and how the unit receives AC power. A conventional 20- or 24-pin ATX motherboard connector is different from proprietary 6-pin or workstation connectors, including some 18-pin-plus-12-pin arrangements. Server or Common Slot supplies may require a backplane or separate control arrangement.
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- 🌟The benchtop power board kit was created to provide quick access to the typical voltages needed when developing physical computing projects (embedded systems).
- 🌟With power light and power switch.
- 🌟Provide quick access to the typical voltages needed including 3.3V, 5V, 12V and -12V
- 🌟Each output channel has replaceable 5A fuse and corresponding ground connection with binding post easy to connect
- 🌟On-board standard 24pin ATX port, power indicator and power switch easy to control ideal to DIY low voltage power supply for developing physical computing projects (embedded systems)
HP support material warns that an HP six-pin motherboard connector may not follow the pinout of a standard auxiliary GPU connector: HP discussion of desktop PSU connector differences. HP workstation documentation also shows that available continuous output can vary with input conditions; a headline wattage is not a promise that every rail can supply that power in every installation: HP Z800 documentation.
- Good candidate: A healthy supply with clearly documented rails, accessible wiring and a verified pinout suited to the intended load.
- Poor candidate: A unit with damaged insulation, corrosion, burned connectors or a failed fan; one that depends on undocumented motherboard control; or one with no trustworthy connector diagram.
- Stop if uncertain: Do not infer pin functions from connector position, wire color or a photo of another HP model. If the exact pinout cannot be verified, keep the PSU in its original system or choose a standard ATX supply.
High wattage is not automatically an advantage. It can mean more short-circuit energy, requiring appropriately rated wiring, fuses, terminals, enclosure and cooling.
Safety essentials
A PC PSU contains mains-side circuitry and capacitors that can retain energy after AC is disconnected. Unplug it before inspection or modification; do not probe or work on the primary side, remove internal barriers, or open the PSU unless qualified to work on mains-powered equipment. Preserve its original AC inlet, earth connection, fuse and safety barriers. Do not obstruct or disconnect the fan: airflow is part of the unit’s thermal design.
The low-voltage outputs can still deliver enough current to overheat thin wire, damage a circuit or cause burns in a short. Fuse each exposed positive rail, choosing a DC-rated fuse below the safe limit of the wire, terminal and intended load. There is no universal fuse value: it depends on the rail rating, wiring, connector and use. The PSU’s built-in protection does not replace suitable output fusing or current limiting for delicate loads.
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- The benchtop power board kit was created to provide quick access to the typical voltages needed when developing physical computing projects (embedded systems).
- With power light and power switch.
- Provide quick access to the typical voltages needed including 3.3V, 5V, 12V and -12V
- Each output channel has replaceable 5A fuse and corresponding ground connection with binding post easy to connect
- On-board standard 24pin ATX port, power indicator and power switch easy to control ideal to DIY low voltage power supply for developing physical computing projects (embedded systems)
ATX rail and signal reference
The following conventional color assignments apply only to a verified ATX-style harness. Confirm against documentation for the exact unit before connecting anything. HP proprietary harnesses may use different colors or signals.
| Wire color | Typical ATX function | Use or caution |
|---|---|---|
| Orange | +3.3 V | Fixed output; confirm its rail rating on the PSU label. |
| Red | +5 V | Fixed output; confirm its rail rating on the PSU label. |
| Yellow | +12 V | Fixed output; confirm its rail rating on the PSU label. |
| Black | Common/ground | Common return for the listed rails. |
| Blue | −12 V | Usually a low-current rail; do not treat it as a high-power negative output. |
| Purple | +5VSB | Standby rail; can remain live whenever AC is connected. |
| Green | PS_ON# | Standard ATX active-low enable for the main rails. |
| Gray | PWR_OK | Power-good signal, not a user power output. |
| Brown or thin additional wire | Possible voltage-sense lead | Do not cut or disconnect without model-specific documentation. |
The ATX design guide defines PS_ON# as active-low and +5VSB as available while valid AC is present: Intel ATX12V Power Supply Design Guide. Never join two positive rails to try to obtain another voltage; doing so can damage the PSU or load.
Convert a confirmed ATX-compatible PSU
This procedure is for a verified standard ATX-compatible HP supply only. It is not a pinout guide for proprietary HP models.
1. Inspect the unit and gather parts
With AC disconnected, inspect for burn marks, bulging or leaking capacitors, damaged insulation, loose or melted connectors, corrosion, chassis damage and a damaged fan. Do not use a visibly damaged unit. Prepare insulated binding posts or shrouded terminals, suitable DC fuse holders and fuses, correctly sized wire, ferrules or crimp terminals, heat-shrink, a control switch, cable strain relief, a multimeter and an enclosure or intact PSU case. A panel meter and DC-DC converter are optional.
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- 1.ATX power supply breakout board supports 3.3V, 5V, 12V and -12V output voltage.
- 2.The voltage output terminals of the ATX power expansion board correspond to each screw terminal.
- 3.At the same time, the panel is also equipped with an acrylic case kit for easy to use.
- 4.Compatible with 3.3V: STM32 MCU, network communication equipment, such as Wi-Fi Bluetooth and other devices, generally for microcontrollers, and some low-power modules, etc. 5V: Raspberry Pi, Banana Pi, Tinker Board, Nano Pi, USB interface, etc.
- 5.Compatible with 12V display driver module, : motor drive, LED light, vehicle equipment with power requirements.
2. Verify the pinout and test the rails
- Use the PSU documentation to identify the ATX connector pins. Do not rely on color alone.
- With AC disconnected, identify a documented ground wire and confirm continuity as appropriate.
- Connect AC with the unit assembled. Put the multimeter’s negative probe on verified ground and measure +5VSB while the main PSU is off.
- Briefly connect the documented PS_ON# signal to ground through a test lead or switch. On standard ATX supplies this active-low signal enables the main rails.
- Measure each intended output with the multimeter. Remove AC before cutting, crimping or soldering.
The ATX guide describes +5VSB as present whenever valid AC is supplied; therefore, switching off the main rails does not necessarily make the unit fully de-energized. The same guide specifies a nominal PWR_OK delay of 100–500 ms after the rails become valid; PWR_OK is a signal, not an output terminal. The standard ATX test method of grounding PS_ON# and measuring the rails is also shown in this ATX conversion guide.
3. Choose which outputs to expose
A practical layout is one common/ground terminal plus separately labeled +3.3 V, +5 V and +12 V terminals. Add −12 V only if needed, and label its low-current limit from the PSU rating. If +5VSB is exposed, use a separate terminal and label it “standby—live whenever AC is connected.” Avoid bringing unused signals such as PWR_OK to output posts.
Bundle parallel wires only when they are the same documented rail, and terminate them securely with suitable hardware. Keep any required sense wire connected to its rail as the manufacturer specifies; a disconnected sense lead can cause incorrect regulation or shutdown.
4. Add switching, fuses and terminals
A beginner-friendly control can switch PS_ON# while leaving the AC side and its original safety parts untouched. Remember that +5VSB may still be present while the main outputs are off. An AC-side switch must be mains-rated and installed with suitable insulation and enclosure design; do not casually reroute mains wiring.
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- 5.PROTECTION --- input reverse connection protection; short circuit protection
Fit a DC-rated fuse in each exposed positive output, sized for the safe capacity of the rail wiring, terminal and intended load. Use insulated binding posts, keep terminals from touching the metal case, deburr holes and add strain relief. Label each output voltage and its current limit from the exact PSU label or documentation, and note that the outputs share a common return.
5. Reassemble and test in stages
- With AC disconnected, check continuity and inspect for accidental shorts between each rail and ground.
- Power on without a load and measure every output at its terminal.
- Test with a small resistive load, then check the switch and each fuse.
- Increase load gradually while monitoring voltage, wiring temperature and fan operation; stay within the exact rail limits.
- Remove the load and confirm the PSU recovers normally before using a valuable circuit.
For a proprietary HP supply, stop and identify the control pins
HP business desktops and workstations can use nonstandard connectors, 12-V-only designs, standby rails, sense pins, motherboard-generated enables or backplane connections. The standard green-to-black ATX jumper applies only to the verified ATX PS_ON# pin; it is not a generic HP power-on trick.
- Photograph and record the PSU label, computer model, spare-part number and connector.
- Find the service manual or electrical diagram for that exact computer and supply family.
- With AC disconnected, use the documentation and careful continuity testing to identify ground; do not guess at a pin.
- Use the exact documentation to identify standby output, enable/control signals and any sense connections.
- Before attaching a load, verify expected output voltages with a multimeter and, where feasible, a current-limited test setup.
If documentation does not establish the pinout, do not short pins or attach output terminals. A standard ATX supply or a purpose-built enclosed DC supply is the safer choice.
Adding an adjustable output
A DC-DC stage can make an adjustable output from a suitable PSU rail, but the converter—not the salvaged PSU—provides the adjustment and any current regulation. A buck converter can step voltage down but cannot produce a regulated output above its input; a +12 V input therefore cannot yield 24 V from a buck-only module. A boost or buck-boost converter is needed when the desired range exceeds the input.
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- Each output channel has replaceable 5A fuse and corresponding ground connection with binding post easy to connect
- Provide quick access to the typical voltages needed including 3.3V, 5V, 12V and -12V.
- Atx breakout board can Compatible with the port: ATX (compatible with partial BTX type)
- The PIN number: 24 pin ; power indicator and power switch easy to control ideal to DIY low voltage power supply for developing physical computing projects (embedded systems)
- Feature: 1. With power output indicator. 2. With module switch to turn off output 3.The output terminal can pass the maximum current. 4. With output protection fuse,four groups correspond to four road output.
Before selecting a module, verify its input range, output range, continuous current rating, cooling needs, efficiency and whether its current limit provides genuine constant-current control. Check whether the display and control circuitry are isolated; do not assume isolation. Place appropriate fusing in the input and output according to the module and wiring requirements. The converter’s credible continuous and thermal ratings—not the PC PSU’s headline wattage—set the practical limit of the adjustable output.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot common problems
The PSU does not start
Possible causes include a proprietary rather than ATX connector, an incorrect enable pin, an AC input or fuse problem, an internal fault, a protection condition, or a missing sense/control connection. Disconnect the load, recheck the exact model documentation and measure standby output. Do not repeatedly short unknown pins; restore the original connector if possible.
It starts and immediately shuts down
Look for a shorted output, excessive inrush current, overcurrent protection, a disconnected sense wire, poor or undersized wiring, a faulty load, or a supply that behaves poorly with the load distribution. Remove loads, check rail-to-ground resistance with power removed, then test with a small resistive load and reconnect one output at a time.
A rail measures incorrectly or the supply seems unstable
Check that the meter is referenced to the correct return and that the pinout and polarity are right. A disconnected sense lead, load-dependent regulation, long output wiring, aging capacitors, overheating, fan failure or an overloaded converter can also cause incorrect or unstable output. Do not attempt to correct a wrong voltage by connecting rails together.
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A motor, lamp or large capacitor trips the supply
Motors, incandescent lamps, heaters and capacitors can draw much more current at startup than their running load suggests. Use a suitably rated fuse and consider soft start, a current-limited DC-DC stage, precharge or a supply designed for the load. Do not assume a PSU that supports the running current will tolerate startup current.
Voltage remains when the main switch is off
On a standard ATX supply this may be +5VSB, which remains available while AC is present. Some HP designs also have standby rails. Label any exposed standby output and unplug the unit before treating it as de-energized.
Reused PSU or purpose-built supply?
| Feature | Reworked HP PSU | Purpose-built bench supply |
|---|---|---|
| Cost | Often low if already available | Higher, depending on model |
| Fixed high current | Can be useful, subject to exact rail limits and wiring | Depends on the selected unit |
| Adjustable voltage | No, unless a suitable converter is added | Usually available on laboratory models |
| Current limiting | Usually absent at the user-adjustable output | Usually included on laboratory models |
| Metering | Optional DIY addition | Usually built in |
| Published noise/ripple specifications | Often not convenient to verify for the conversion | Typically specified by the manufacturer |
| Enclosure and safety integration | Your responsibility during modification | Factory designed, though installation still matters |
| Best suited to | Fixed rails, PC projects, LEDs and suitable motors | Sensitive electronics and controlled experiments |
Reuse the HP supply when the pinout is documented, fixed rails meet the need and you can install appropriate protection. Choose a laboratory supply when controlled current limiting, accurate adjustment or repeatable measurements matter more than obtaining fixed current at low cost.
Quick Recap
Final build checklist
- Exact HP model and PSU part number recorded.
- Connector type and pinout verified from reliable documentation.
- No unknown pins shorted or connected to terminals.
- Fan connected and airflow unobstructed.
- Each exposed positive rail fused for the wiring and intended use.
- Terminals insulated, secured and clearly labeled with voltage and current limits.
- Any standby output labeled as potentially live while AC is connected.
- No exposed mains conductors; original earth and safety barriers preserved.
- Outputs tested with a multimeter and a controlled load before use.
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