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How to check a used power supply
The component with the worst risk-to-saving ratio on the whole marketplace. It ages on a shelf as readily as in a machine, its failures are invisible until they are not, and it is the only part that can take everything else with it on the way out.
The short answer
For most people the honest answer is buy new. A power supply is the cheapest part to replace with a warrantied unit, and the money you save used is small next to what it can cost you. If you are buying one anyway, the cable warning below is the single most important paragraph on this page.
Get these first
HWiNFO64FreeWindowsEvery sensor on the machine, plus CSV logging. The one tool to install first.OCCTFree tierWindowsPower, 3D, VRAM and memory tests that detect calculation errors, not just crashes.CybeneticsFreeWebMeasured efficiency, ripple and noise for specific power supplies, across thousands of load points.Hardware BustersFreeWebIndependent power-supply reviews and ranked picks from the lab behind Cybenetics.PSU databaseFreeWebMaps a retail power-supply model to the OEM platform actually inside it. Brands rebadge; platforms do not.PCPartPickerFreeWebCatches clearance and compatibility problems — cooler height, radiator mounts, case and board fit — before you pay.
If you are buying one anyway
- Read the label properly. Model, total wattage, the +12V rail rating in amps, and the manufacture date — most units print one. A unit built eight years ago is eight years old however gently it was used, because electrolytic capacitors age on the shelf.
- Look up the platform, not the brand. Brands rebadge units built by a handful of OEMs, and the platform inside decides the quality. Cybenetics publishes measured efficiency, ripple and noise across thousands of load points rather than the four that an 80 PLUS badge covers, Hardware Busters reviews specific units, and the PSU database maps models to platforms. A gold badge on a bad platform is still a bad unit.
- Check which protections it lists — OCP, OVP, UVP, OPP, SCP and OTP. A unit without over-current and short-circuit protection is precisely the unit that passes a fault along to your motherboard instead of shutting down. This matters far more than the efficiency rating.
- Confirm every original cable is present, and count the PCIe or 12VHPWR connectors against what your graphics card actually needs. Use native cables, avoid running one cable to two eight-pin plugs on a high-draw card, and treat bundled adapters as a question rather than a solution.
- Ask about warranty and get the receipt. Good units carry seven to twelve years, but the clock starts at the original purchase and some manufacturers will only honour it for the original purchaser. “Five years left” is worth nothing without the paperwork that proves it.
- Load-test it in a machine, not on a bench. Fifteen minutes of OCCT’s combined power test with the processor and graphics card loaded together is the condition that finds a tired unit. Watch for a reboot, a shutdown, or a click from the unit itself. Board 12V sensors are crude, but a large sag under load still shows up.
- Listen and smell. Coil whine that changes pitch with load is common and mostly harmless. A rattling fan is a wear item. The smell of hot varnish, or of fish, is neither — that is a unit telling you something.
- Check the connectors under a torch, especially the 12VHPWR or 12V-2x6 plug on anything recent. Browning, melted keying or a plug that no longer clicks home firmly is the end of the conversation.
Danger
Modular cables are not interchangeable. Not between brands, and not always between two generations from the same brand. The sockets are the same physical connector, and manufacturers assign the pins differently — so a cable that fits perfectly can deliver 12 volts to a pin the device expects to be ground. The result is a dead drive, a dead board, or a fire, and no warranty covers it. Only ever use the cables that shipped in the box with that exact unit. If a used supply arrives without its own cables, the cables are not what is missing — safe use of the unit is.
Worth knowing
The badge on the box measures efficiency, not safety and not stability. A unit can be 80 PLUS Gold and still have poor voltage regulation, no over-current protection and a fan that dies in a year. Efficiency tells you about your electricity bill; the protections list and an independent review tell you about your hardware.
What to measure
Higher is better▲Higher is betterLower is better▼Lower is betterMust be zero∅Must be zeroMust match the spec=Must match the spec
Power supply numbers that matter
| Metric | Which way | What it tells you | Healthy looks like |
|---|---|---|---|
| Manufacture date on the label | Lower is better | How old the capacitors are, regardless of hours run. | Under about five years for a unit you intend to trust with other hardware. Past eight, the saving is not worth it. |
| Warranty remaining, and transferable | Higher is better | Whether anybody but the seller could ever claim it. | Years left and the original receipt in hand. Without the receipt, assume none. |
| Protections listed | Must match the spec | Whether the unit shuts down on a fault or passes it downstream. | OCP, OVP, UVP, OPP, SCP and OTP all present in the specification. |
| +12V rail rating vs your draw | Higher is better | Almost all of a modern system draws from the 12V rail. | Comfortable headroom over your measured wall draw, with room for the transient spikes a modern graphics card produces. |
| Reboots or shutdowns under combined load | Must be zero | The clearest single test of a used unit. | None, in fifteen minutes with the CPU and GPU loaded together. |
| 12V under combined load | Must match the spec | Voltage stability when everything pulls at once. | Within about 5% — roughly 11.4 to 12.6 V. Look for a large sag rather than trusting small movements. |
| Original cables, all present | Must match the spec | The only cables that are safe with this unit. | Every one, confirmed as shipped with this exact model. See the warning below — this is not a convenience issue. |
| Connector condition | Must be zero | Heat damage at any plug, especially 12VHPWR. | No browning, no melting, and every connector still clicks home. |
Walk away if
Walk away if
- It arrives without its own cables, or with cables the seller “thinks” are the right ones.
- Any browning or melting at a connector.
- A reboot the instant a combined CPU and GPU load starts.
- No manufacture date anywhere, or one more than about eight years ago.
- A no-name unit with no independent test data in existence.
- A burning smell, a scorch mark, or an owner who mentions a bang.
- A “600W” unit whose +12V rail adds up to nothing like 600W.
What each fault is worth
Bring the measurement, not the opinion. Name the fault, name the fix, name what the fix costs — that is a solvable problem with two acceptable answers, which is what makes it work.
| What you found | What it actually costs | What to ask for |
|---|---|---|
| Missing original cables | The unit is not safely usable. This is not a discount item. | Do not buy it. A replacement cable set from the maker, if one exists, or walk away. |
| Over five years old | Capacitors that have aged whether or not it was run. | A large reduction — and ask yourself what a new warrantied unit costs. |
| No warranty or no receipt | Every future failure is yours. | Meaningfully less than the same unit with paperwork. |
| Rattling fan | A wear item, and on some units a proprietary size. | The cost of the fan, if one is available at all. |
| Group-regulated or no-name platform | Poor voltage regulation on modern loads. | Treat as a spare-parts purchase, not a system power supply. |
Ready to go looking?
Take the checklist with you, then browse what is listed. Everything on this page works just as well the other way round when you are the one selling.
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