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For one stock GeForce 7900 GT, use a healthy, reputable 400 W PSU with at least about 18–20 A available on +12 V. For one GeForce 7900 GTX, plan on a quality 350–400 W PSU and roughly 22–26 A on +12 V, with extra margin for a power-hungry CPU or several drives. Both standard cards normally require one 6-pin PCIe auxiliary connector.
Those are whole-system planning figures, not the graphics card’s isolated consumption. The correct decision comes from the PSU label, connector, system hardware, and the unit’s condition—not the printed wattage alone.
Quick requirements
| Card | Practical single-card PSU target | +12 V target | Auxiliary power | Period measured card load |
|---|---|---|---|---|
| GeForce 7900 GT | Quality 400 W or greater | At least 18 A; 20 A or more is preferable for an overclocked model | 1 × 6-pin PCIe | 48.6 W under 3D load (Tom’s Hardware test) |
| GeForce 7900 GTX | Approximately 350–400 W or greater, depending on the system | Approximately 22–26 A or more | 1 × 6-pin PCIe | 84.0 W under 3D load (Tom’s Hardware test) |
These values are qualified by the exact board, processor, drives, overclock, and PSU condition. EVGA’s archived 7900 GT specification lists 400 W/500 W-or-greater supplies with 18 A/28 A on +12 V for different configurations (EVGA specification). A period recommendation reproduced in the AnandTech archive gives the 7900 GTX approximately 350–400 W and 22–26 A on +12 V (AnandTech archive).
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Standard card
Use a quality 400 W unit as the practical minimum, with at least 18 A on +12 V. A native 6-pin PCIe lead is required for normal operation. The EVGA figure is vendor-specific, so check the label or manual for a non-EVGA board.
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Factory-overclocked card
Allow more margin for a 7900 GT CO or another factory-overclocked variant. EVGA’s 7900 GT CO specification lists 400 W/500 W or greater and 20 A/28 A on +12 V (EVGA 7900 GT CO specification). Use the board partner’s requirement when it is available.
7900 GTX: historical requirements
For a single 7900 GTX, period guidance was approximately 350–400 W with 22–26 A on +12 V. Treat that as a historical planning range rather than a guarantee: a Pentium D, Athlon 64 FX, multiple disks, or overclocking can make a stronger supply sensible. The card uses one 6-pin PCIe connector.
Why measured GPU power is lower than the PSU recommendation
| Measurement | 7900 GT | 7900 GTX |
|---|---|---|
| Card idle | 23.9 W | 33.8 W |
| Card 3D load | 48.6 W (about 4.1 A) | 84.0 W (about 7.0 A) |
| Whole-system idle | 93 W | 105 W |
| Whole-system 3D load | 163 W | 206 W |
Tom’s Hardware measured the card and the complete test computer separately (card measurements; system measurements). The PSU must supply the CPU, motherboard regulators and chipset, memory, drives, fans, USB devices, other cards, and startup or load transients. A wall-meter result is therefore not the GPU’s isolated draw. Another period measurement reported about 48.42 W for the GT and 84.21 W for the GTX under load (AnandTech archive).
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Read the PSU label, not just the wattage
- Find the combined +12 V rating. If separate rails are listed, use the manufacturer’s combined limit rather than adding rail numbers blindly.
- Confirm a native 6-pin PCIe cable, or verify that a supplied adapter is appropriate.
- Check the manufacturer, model, approximate age, and signs of overheating or capacitor failure.
- Account for the CPU, number of drives, additional cards, and any overclock.
| Example label | Assessment |
|---|---|
| 400 W, +12 V rated 30 A | Generally a good candidate for one GT or GTX if healthy and properly connected. |
| 500 W, +12 V rated only 17 A | Potentially unsuitable despite the higher headline wattage. |
| 350 W, +12 V rated 25 A | May work in a modest single-card system, but age, quality, and connector availability decide it. |
6-pin PCIe connector and adapters
Both cards are listed with one 6-pin PCIe connector (Tom’s Hardware connector table). The slot supplies part of the power, but the auxiliary plug is still required.
- Prefer a PSU with a native PCIe 6-pin lead.
- A properly wired Molex-to-PCIe adapter can change the plug format when the PSU itself is suitable; it adds no capacity.
- Avoid improvised splitters and overloaded peripheral cables.
- Do not substitute an 8-pin CPU/EPS cable. A 6+2 PCIe cable may be used as a 6-pin PCIe cable with the extra two pins left unattached.
SLI, overclocking, and unusual systems
Single-card figures do not apply to two-card SLI. SLI adds a second GPU, a second auxiliary connector, motherboard and chipset load, and substantially more heat. Choose a considerably stronger, high-quality PSU after accounting for the exact CPU and drives; do not multiply only the measured GPU wattage. The same caution applies to CPU or GPU overclocking.
How to judge an existing PSU
- For one 7900 GT, look for at least 400 W and about 18–20 A or more on +12 V.
- For one 7900 GTX, look for about 350–400 W and roughly 22–26 A or more on +12 V.
- Confirm one 6-pin PCIe connection.
- Reject no-name units, missing or implausibly low +12 V ratings, severe age, fan failure, electrical noise, burning smells, or bulging capacitors.
- Replace rather than gamble when the system already reboots or loses video under 3D load.
A modern quality ATX supply can generally power these cards, provided its physical connectors, +12 V capacity, and case or motherboard compatibility are suitable. A 400–550 W replacement is usually ample; extra wattage alone does not fix a weak rail or degraded unit.
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Diagnosing instability
Symptoms that can involve power
- Reboot or shutdown when a 3D application starts
- Black screen, driver crash, or “power connector not attached” warning
- Corruption that appears only under load
- Failure to boot after installing the card
- Stability returning when the GPU is underclocked
Symptoms that point elsewhere
Artifacts in BIOS or at idle, a seized fan, damaged card capacitors, persistent memory errors, or overheating from dried thermal compound can indicate a failing card. A new PSU cannot repair defective GPU or VRAM hardware.
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- Identify the exact card and confirm the 6-pin plug is connected; clean dust and verify that the fan spins freely.
- Record the PSU wattage, +12 V ratings, combined limit, model, age, and cable types.
- Return the CPU and GPU to stock clocks and use a suitable legacy driver.
- Run a 3D application while observing temperature and the failure pattern.
- Substitute a known-good quality PSU, then test the card in another compatible system or test the system with another card.
A basic PSU tester can find gross connector or voltage faults but cannot prove stability under sustained 3D load. A wall meter measures total input and does not reveal ripple or connector resistance.
Bottom line for a purchase decision
Choose a healthy, reputable PSU with the required 6-pin PCIe connection and adequate combined +12 V output. For one stock 7900 GT, 400 W and about 18–20 A is a sensible floor; for one 7900 GTX, use the historical 350–400 W and 22–26 A range with additional margin for demanding hardware. Treat SLI, factory overclocking, and aged supplies as separate cases.
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