Test your power supply with a multimeter, paperclip test, or by observing whether your PC boots and stays stable under load

A failing power supply often looks like a dead motherboard or bad RAM — your PC won't start, restarts randomly, or shuts down under heavy use. Before you buy a replacement, you can narrow down whether the power supply is actually the problem. The fastest method is the paperclip test, which takes five minutes and costs nothing. If that passes, a multimeter tells you whether the voltages are correct. If you want to see how the supply behaves under real load, you can run stress tests while monitoring power draw.

Key Takeaways

  • The paperclip test powers on the supply outside the PC to confirm it produces any voltage at all — if it fails, the supply is dead.
  • A multimeter checks whether the supply outputs the correct voltage on each rail (12V, 5V, 3.3V), which narrows down whether it is failing partially or completely.
  • Stress tests like Prime95 or FurMark load the CPU and GPU heavily while you watch whether the PC stays stable or crashes, revealing power delivery problems under demand.
  • A power supply that passes the paperclip test but fails a multimeter check or crashes under load is degraded and should be replaced.
  • Unplug the PC and wait 30 seconds before opening the case or touching the power supply to discharge residual voltage.

The Paperclip Test: Checking Whether the Supply Powers On

The paperclip test is the first step because it tells you whether the power supply is completely dead or at least producing voltage. You do not need any tools except a paperclip and your hands.

Unplug the PC from the wall outlet and wait 30 seconds. Open the case and locate the 24-pin ATX connector — the large rectangular plug that connects the power supply to the motherboard. Do not disconnect it yet. Find a paperclip and straighten one end slightly so you can insert it into the connector holes.

Look at the 24-pin connector from the front (the side facing out of the case). The green wire is usually in pin 16 (counting from the left, starting at 1). The black wire next to it is ground. Bend your paperclip into a U shape and insert one end into the hole above the green wire and the other end into the hole above the black wire next to it. Plug the PC back in and flip the power supply switch to ON. If the power supply fan spins, the supply is producing voltage and is not completely dead. If nothing happens, the supply is likely failed.

Turn off the power supply, unplug the PC, and remove the paperclip. Wait 30 seconds before proceeding.

Using a Multimeter to Check Voltage Output

A multimeter measures the actual voltage on each rail of the power supply. You can buy a basic digital multimeter for $10 to $20 at any hardware store. This test tells you whether the supply is outputting the correct voltage (within tolerance) or whether one or more rails are sagging.

Set your multimeter to DC voltage mode (usually marked with a V with a line and dots, or "DCV"). Unplug the PC and wait 30 seconds. Leave the 24-pin connector plugged into the motherboard. Locate the power supply cables running from the supply to the motherboard and other components. You are looking for the colored wires: red (12V), yellow (12V), orange (3.3V), and black (ground).

Plug the PC in and turn on the power supply switch. Do not press the power button on the case — the supply should power on from the paperclip test. Touch the black probe of the multimeter to any black wire (ground). Touch the red probe to a red wire and note the reading — it should be between 11.4V and 12.6V. Test a yellow wire next — it should also read 11.4V to 12.6V. Test an orange wire — it should read 3.14V to 3.46V. Test a purple wire if present — it should read 4.75V to 5.25V.

If any reading is outside these ranges, the supply is degraded. If all readings are within range, the supply is at least producing correct voltage at idle. Turn off the power supply and unplug the PC.

Stress Testing to Find Problems Under Load

A power supply can pass the paperclip test and multimeter check but still fail when the PC is under heavy load. Stress testing reveals whether the supply can deliver stable power when the CPU and GPU are working hard.

Boot into Windows normally. read and run Prime95 (free, from mersenne.org) or FurMark (free, from geeks3d.com). Prime95 loads the CPU; FurMark loads the GPU. Run one of these for 15 to 30 minutes while watching for crashes, freezes, or unexpected restarts. If the PC stays stable, the power supply is likely handling load correctly. If it crashes, restarts, or shows artifacts on screen, the supply may not be delivering enough power under demand.

You can also monitor power draw and temperatures during the test using free tools like HWiNFO (from hwinfo.com). This shows you the actual power consumption and whether voltages are sagging under load — a sign of a failing supply.

What Each Test Result Means

If the paperclip test fails (fan does not spin), the power supply is dead and must be replaced. There is no point testing further.

If the paperclip test passes but the multimeter shows voltages outside the ranges listed above, the supply is degraded and should be replaced. It may work for a while but is unreliable.

If the multimeter readings are correct but the PC crashes or restarts under stress test load, the supply may be failing under demand. This is harder to diagnose because the supply is producing correct voltage at idle but cannot sustain it when power draw spikes. Replacing the supply is usually the safest fix.

If all three tests pass, the power supply is likely not the problem. Look at the RAM, motherboard, or storage drive instead.

Safety Precautions When Testing

Power supplies store voltage even when unplugged. Always unplug the PC and wait 30 seconds before opening the case or touching the power supply. This discharges the capacitors inside.

Do not touch the power supply components directly with bare hands if you are standing on a conductive surface like a metal workbench. Wear an anti-static wrist strap (a few dollars at any electronics store) clipped to the case to ground yourself.

Do not test a power supply that is visibly damaged, burned, or leaking. Replace it when ready.

When to Replace Instead of Test

If your PC is more than five to seven years old and the power supply is the original one, replacement is often cheaper and faster than diagnosis. Power supplies degrade over time, and a used or refurbished supply from a reputable seller costs $30 to $60 for a basic 500W unit.

If you are uncomfortable opening the case or using a multimeter, take the PC to a local repair shop. Most will test the power supply for $20 to $50 and tell you whether it needs replacement.

Frequently Asked Questions

Can I test the power supply while it is still connected to the motherboard?

Yes. The paperclip test and multimeter test both work with the 24-pin connector plugged in. You do not need to disconnect anything. Just unplug the PC from the wall and wait 30 seconds before you start.

What if the multimeter shows the correct voltage but the PC still crashes?

The supply may be failing under load even though it outputs correct voltage at idle. Run a stress test like Prime95 or FurMark for 30 minutes. If the PC crashes during the test, the power supply is likely the problem. If it stays stable, look at RAM, storage, or drivers instead.

Do I need a fancy multimeter or will a cheap one work?

A basic $10 to $20 digital multimeter is fine for this test. You only need to measure DC voltage, which every multimeter can do. Expensive models add features you do not need for power supply testing.

Is the paperclip test safe?

Yes, as long as you unplug the PC first and wait 30 seconds. The paperclip shorts two pins that are designed to be shorted together — that is how the power button works. You are not creating a dangerous short circuit.

What if the power supply fan spins but the PC still will not start?

The supply is producing some voltage, but the motherboard may not be receiving it correctly. Check that the 24-pin connector is fully seated and that the 8-pin CPU power connector (near the CPU socket) is also plugged in. If both are connected and the PC still will not start, the motherboard or CPU may be the problem, not the supply.