Start with the paperclip test to check if your power supply turns on

The fastest way to know if your power supply is dead is the paperclip test. Unplug the power supply from the wall and from your motherboard. Locate the 24-pin ATX connector — the large plug that connects to your motherboard. Look for the green wire and any black wire in that connector.

Straighten a paperclip and insert one end into the socket holding the green wire, and the other end into a socket holding a black wire next to it. Plug the power supply back into the wall outlet. If the fan spins, your power supply is getting power and can turn on. If nothing happens, the power supply itself may be faulty. Unplug it when ready and remove the paperclip.

This test tells you whether the power supply responds to power at all. It does not tell you whether the voltages are correct or whether it can handle a full load. Those require a multimeter.

Key Takeaways

  • The paperclip test shows whether your power supply fan spins when powered on, which rules out a completely dead unit in under a minute.
  • A multimeter set to DC voltage can measure the actual output on the 24-pin motherboard connector and the 8-pin CPU power connector to confirm voltages are within range.
  • The load test — running your PC under heavy use while monitoring temperatures — reveals whether the power supply fails under real-world demand.
  • If your power supply passes the paperclip test but your PC crashes or won't start, the problem is usually insufficient power under load, not a dead supply.
  • Bulging or leaking capacitors, burn marks, or a burning smell mean the power supply should be replaced when ready, regardless of test results.

Use a multimeter to measure voltage on the main connectors

A multimeter is a handheld tool that costs between $15 and $40 and measures electrical voltage. Set it to DC voltage (marked with a V and a straight line with dots underneath). You do not need an expensive one — a basic digital multimeter works fine for this test.

With the power supply still plugged in and the paperclip still in place (keeping the fan running), touch the multimeter's red probe to the red wire in the 24-pin connector and the black probe to a black wire. You should read between 4.8 and 5.2 volts. Test the yellow wire against black — that should read between 11.4 and 12.6 volts. Test the orange wire against black — that should read between 2.97 and 3.63 volts.

These ranges are the official tolerances. If your readings fall outside them, the power supply is not regulating voltage correctly and should be replaced. If all three readings are within range, move to the 8-pin CPU power connector (the smaller plug near the top of the motherboard socket). Test red against black on that connector — it should also read 11.4 to 12.6 volts.

Write down your readings. If they drift as you watch, or if they are close to the edge of the acceptable range, the power supply may be failing and worth replacing even if it technically passes.

Run a load test to see if the power supply holds up under real use

A multimeter test with the paperclip shows what the power supply does at idle. A load test shows what it does when your PC is actually working. Reassemble your PC, plug everything back in normally, and boot into Windows.

Open a program that stresses your CPU and GPU at the same time. Prime95 (free, downloadable from mersenne.org) stresses the CPU. FurMark (free, downloadable from geeks3d.com) stresses the GPU. Run Prime95 for 30 minutes while monitoring your CPU temperature with a tool like HWiNFO (free, downloadable from hwinfo.com). If your PC crashes, restarts, or shuts down during the test, your power supply is likely failing under load.

Watch for sudden shutdowns without error messages — that is a classic sign of power supply failure. Crashes with error messages or blue screens usually point to RAM or drivers instead. If the test completes without incident and temperatures stay below 80 degrees Celsius, your power supply is handling the load.

Check for physical damage that means replacement is urgent

Before you run any electrical tests, look at the power supply itself. Open your PC case and inspect the power supply unit. Look for bulging or leaking capacitors on the circuit board inside — they look like small cylinders with domed or split tops. Bulging capacitors fail over time and are a sign the power supply is aging out.

Check for burn marks, scorch marks, or discoloration on the circuit board or connectors. Smell the power supply — a burning or acrid smell means stop when ready and do not use it. These are signs of internal failure that can damage other components or create a fire risk.

If you see any of these, replace the power supply. Do not run tests on it. Physical damage is enough reason on its own.

Understand what wattage your PC actually needs

Many people replace a power supply with one that is too weak for their system. Before you buy a replacement, add up the power draw of your components. Your CPU has a TDP (thermal design power) listed on the manufacturer's spec sheet — Intel and AMD both publish these. Your GPU has a power requirement listed in the manual or on the product page.

Add those two numbers and multiply by 1.5. That gives you a rough minimum. A CPU with a 125-watt TDP and a GPU with a 250-watt requirement would need at least 562 watts (125 + 250 = 375, times 1.5 = 562). In practice, most people buy a power supply 100 to 200 watts above that minimum to leave headroom.

A power supply rated for 650 watts that is actually failing will not work better if you replace it with a 750-watt unit. The problem is the old supply itself, not the wattage. Buy a replacement that matches your actual system needs, not just a bigger number.

Know the difference between a failing supply and a PC that won't start

A PC that will not start is not always a power supply problem. If your power supply fan spins when you press the power button, the supply is delivering some power. The issue is usually elsewhere — a bad motherboard, a disconnected power cable, or a faulty power button.

If the fan does not spin at all when you press the power button, and the paperclip test shows the fan does spin when you manually jump the connector, then the motherboard is not signaling the power supply to turn on. That points to a motherboard problem, not a power supply problem.

If the fan spins but your PC crashes under load, or if it restarts randomly during normal use, the power supply may be failing even though it technically turns on. Run the load test to confirm.

Frequently Asked Questions

Can a power supply fail partially and still work sometimes?

Yes. A failing power supply may work fine at idle but shut down under load, or it may work for weeks and then fail suddenly. If your PC crashes or restarts only during gaming or heavy work, and the load test reproduces the problem, the power supply is the likely culprit. Partial failures are common as capacitors age.

Is it safe to do the paperclip test?

The paperclip test is safe as long as you use a paperclip, not a metal screwdriver or wire. A paperclip is thin enough that it will not cause a short circuit. Always unplug the power supply from the wall before inserting or removing the paperclip, and always remove it before you reconnect the power supply to your PC normally.

What if my multimeter readings are slightly outside the acceptable range?

If your readings are off by a small amount — say 5.3 volts instead of 5.2 — and your PC runs without crashing, the power supply is aging but not yet critical. Monitor it over the next few weeks. If readings drift further or your PC becomes unstable, replace it. If readings stay the same and your PC is stable, you can keep using it.

Do I need to test every connector on the power supply?

No. Testing the 24-pin motherboard connector and the 8-pin CPU connector covers the main power rails. If those are within range, the other connectors (SATA, PCIe, Molex) are usually fine. You can test them if you want to be thorough, but it is not necessary for a basic diagnosis.

What should I do with an old power supply after I replace it?

Power supplies contain materials that should not go in the trash. Take it to an electronics recycling center, a Best Buy (which accepts power supplies for free), or a local computer repair shop. Many will take it at no charge. Do not throw it in the garbage or leave it on the curb.