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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Yes—you can make a bipolar supply such as +12 V, 0 V, and −12 V from two single-output DC supplies, but only if their outputs are isolated and the manufacturers permit series operation. Connect the positive terminal of one supply to the negative terminal of the other; that junction is the circuit’s 0 V reference. The two outer terminals provide about 24 V between them.
Do not assume two matching adapters are safe to stack. An earth, USB, or other ground connection can short part of the series arrangement. Verify the supplies’ documentation before wiring them.
Choose the output you need
“Dual power supply” can mean a split supply with positive and negative rails, or simply two supplies connected to make a higher voltage. Those configurations use series wiring. A parallel connection is a different arrangement intended to increase current, not to create a negative rail.
| Goal | Connection | Result | Main limitation |
|---|---|---|---|
| Create +V, 0 V, and −V | Series; use the junction as the common reference | Bipolar rails | Outputs must be isolated and suitable for series operation |
| Increase voltage | Series; use the two outer terminals | Output voltages add | Current is limited by the lower-rated supply |
| Increase current | Parallel, only when supported | One higher-current output | Requires compatible supplies and suitable current sharing |
| Keep outputs independent | Do not interconnect them | Separate outputs | A shared reference exists only if deliberately added |
For instance, two 12 V supplies in series can provide approximately +12 V, 0 V, and −12 V when the midpoint is used as common. The outer terminals measure approximately 24 V apart. Series operation adds voltages, subject to the supplies’ isolation, floating-voltage, current, and reverse-voltage limits; see Keysight’s power-supply guidance.
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Check that the supplies are compatible
Read the manuals or datasheets for both exact models before connecting them. Look for wording such as “floating output,” “output-to-ground isolation,” or “series operation permitted.” A two-wire DC output does not, by itself, prove that the output floats. A continuity check is not proof of isolation because internal components can affect the reading; rely on the manufacturer’s specifications.
- Isolation and grounding: Confirm each output is isolated from its AC input, protective earth, and the other supply as required for the proposed series connection.
- Series limits: Check the maximum output-to-earth or floating voltage, reverse-voltage restrictions, and any specific series-connection rules.
- Shared connections: Identify earth, USB, communications, shields, and other connections that could join an output to ground or to the other supply.
- Ratings and behavior: Prefer identical supplies with matching voltage and current ratings. If using different models, verify that their regulation, protection, startup behavior, and ratings are compatible.
- Load and return voltage: Check current limits and whether the load can send energy back into a supply. Beckhoff’s guidance, for example, warns against return voltage at supply outputs: Beckhoff series-connection notes.
Manufacturers document series operation for some isolated outputs, not for every product. RIGOL’s DP2000 guide, for example, discusses isolated channels and series connections. That does not establish that an unrelated adapter is suitable.
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Wire two supplies for positive and negative rails
This example assumes two compatible, isolated 12 V DC supplies. Supply A provides the negative rail; Supply B provides the positive rail. The joined terminals form the circuit’s common reference.
Supply A (−) ─────────────── −12 V rail
Supply A (+) ─────┐
├───────── 0 V / circuit common
Supply B (−) ─────┘
Supply B (+) ─────────────── +12 V rail- Turn both supplies off and disconnect the load.
- Set both outputs to the same nominal voltage. For this example, set each to 12 V.
- Connect Supply A’s positive terminal to Supply B’s negative terminal. This junction is 0 V or circuit common.
- Connect Supply A’s negative terminal to the circuit’s negative rail, and Supply B’s positive terminal to its positive rail.
- Connect the circuit’s reference or common to the midpoint. Confirm that the circuit is designed for the resulting positive and negative voltages before powering it.
The nominal readings are approximately +12 V from the midpoint to the positive rail, −12 V from the midpoint to the negative rail, and 24 V between the outer rails. Actual readings depend on each supply’s regulation, tolerance, and load.
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Use the same series connection for a higher single voltage
To obtain approximately 24 V from two 12 V supplies, use the outer terminals and leave the midpoint unused:
Supply A (−) ─────────────── 24 V negative
Supply A (+) ─────┐
├───────── unused midpoint
Supply B (−) ─────┘
Supply B (+) ─────────────── 24 V positiveProtect the unused junction from accidental contact. Two 12 V, 2 A supplies in series provide approximately 24 V with no more than 2 A available—not 4 A. Series wiring raises voltage; it does not add the current ratings. Keysight’s series and parallel supply guidance describes these distinct configurations.
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Test the rails before connecting the circuit
- With power off, confirm the midpoint connection and check that no unintended earth, USB, instrument, or load connection joins the supplies.
- Turn on the supplies without the final load, following any manufacturer-required startup sequence.
- Using a multimeter set to measure DC voltage, measure from the midpoint to the positive rail. Expect approximately +12 V for the example.
- Measure from the midpoint to the negative rail, keeping the meter’s red lead at the midpoint. Expect approximately +12 V. With the red lead on the negative rail and black lead at the midpoint, the reading should be approximately −12 V.
- Measure between the outer rails. Expect approximately 24 V.
- Only after confirming polarity and readings, connect the load. Add load gradually where practical, then check both rails under the expected operating conditions and during startup.
A negative meter reading can simply mean the probes are reversed. A near-zero or unexpected reading, a supply entering protection, or unusual heating calls for switching off and checking the wiring and compatibility before proceeding.
Understand the current and grounding limits
Current on each rail
Supply A powers the negative rail and Supply B powers the positive rail. Treat each rail as limited by its own supply’s current rating, subject to thermal derating, minimum-load requirements, protection behavior, and regulation under load. Equal nominal voltages do not guarantee equal regulation. Circuits that draw substantially different current from the two rails may cause one rail to sag or one supply to trip; measure under the actual expected load, especially for precision applications.
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0 V is not automatically protective earth
The midpoint is the circuit’s 0 V reference. Protective earth is a safety connection to the chassis or building wiring. They are different functions, even if a design intentionally bonds them at one point. Connect the midpoint to earth only when the system design and supply documentation allow it. An earth-grounded oscilloscope, PC, or USB device can create an unintended connection, so account for all attached equipment before energizing the stack. Mean Well’s series/parallel and grounding guidance notes that grounding and leakage-current considerations depend on the product and system.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Avoid common failure modes
- Stacking outputs that are not isolated: If an output is tied to earth or another common, the series junction can short a supply or create an unsafe condition.
- Confusing series and parallel wiring: Joining positive to positive and negative to negative is parallel operation, not a split-rail supply. If output voltages differ, current may flow between supplies.
- Ignoring reverse voltage or floating limits: The supplies’ documentation must allow the voltages and conditions imposed by the stack. Some products prohibit series operation or reverse voltage.
- Assuming simultaneous or independent startup is harmless: A supply that starts or shuts down first may expose the other to conditions it cannot tolerate. Switch them together where practical, and follow manufacturer sequencing instructions. Avoid connecting or disconnecting series terminals while energized.
- Letting a load backfeed: Batteries, charged capacitors, motors, inductors, or another supply can drive current back into an output, particularly during shutdown or a fault. Verify that the supplies and system can handle this.
- Overlooking mains safety: Do not open or modify mains-powered adapters unless qualified to work on hazardous voltages. Use certified enclosed supplies, suitable wiring, fusing, strain relief, insulation, and earthing as required.
- Ignoring noise: Switching supplies can add ripple, common-mode noise, or switching artifacts. Sensitive analog or audio circuits may need a suitably designed filter, regulator, or lower-noise supply.
Should you use ordinary wall adapters?
Only use them if the exact models are documented as suitable. Before stacking two adapters, confirm they are DC supplies with compatible ratings, isolated floating outputs, permitted series operation, and no unwanted connection through earth, USB, the load, or other equipment. Make sure the load is within each adapter’s rating and that wiring cannot be misconnected.
Do not assume USB chargers, PC power supplies, or multi-output consumer supplies can be stacked. Their negatives, shields, or multiple outputs may share a reference, and their protection or backfeed behavior may not support series use. If the documentation does not establish compatibility, choose another arrangement.
Quick Recap
Choose a purpose-built supply when the application demands it
- For lab work: A dual-output bench supply is often the clearer option when you need adjustable positive and negative rails, current limiting, metering, coordinated controls, or programmable operation. Check channel isolation, tracking, series mode, and output-to-earth ratings in the manual.
- For permanent equipment: Use a purpose-built enclosed dual-output supply with documented safety, grounding, protection, and noise characteristics appropriate to the design. Verify the exact model; product-family guidance does not guarantee that every model supports series operation.
- For a DC input source: An isolated DC-DC converter may provide bipolar rails if its channels and ratings are designed for the job.
- For a low-current virtual midpoint: A rail splitter can create a reference for some analog circuits, but it is not equivalent to a real negative supply: its ability to source and sink current is limited. A charge pump or inverter can also provide a negative rail, typically with current and noise trade-offs.
- For a traditional linear design: A center-tapped transformer can form a split supply, but the rectification, capacitors, regulation, fusing, thermal design, and mains-safety work make this a separate power-supply design task.
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