Start with the basics: listen, look, and feel

The fastest way to check your power supply is to watch what happens when you turn your PC on. A working PSU will spin its fan (you'll hear a faint whir), the power light on your case or monitor will come on, and your motherboard will light up. If nothing happens when you press the power button, or if your PC shuts down randomly, your PSU may be failing.

Before you assume the worst, make sure the power cable is plugged in firmly at both the wall outlet and the back of your PSU. Check that the power switch on the back of the PSU itself is flipped to the ON position—this is straightforward to miss. If the cable feels warm to the touch or smells like burning plastic, stop using the PC when ready and unplug it; that's a sign of a real problem.

Listen for the fan. A healthy PSU fan will spin up when the PC boots and may speed up or slow down depending on how hard your system is working. If you hear grinding, clicking, or squealing, the fan bearing is likely worn out and the PSU should be replaced.

Key Takeaways

  • A working PSU will spin its fan, light up your motherboard, and respond to the power button; silence or no response usually means a problem.
  • Check the power cable connection and the physical ON/OFF switch on the PSU itself before assuming failure.
  • Use the paperclip test to see if the PSU powers on independently, which tells you whether the problem is the PSU or something else in your PC.
  • Monitor your PC's temperature and watch for random shutdowns or restarts, which often point to a PSU that cannot deliver stable power.
  • If your PSU is more than five years old and showing signs of trouble, replacement is usually cheaper and safer than repair.

The paperclip test: checking the PSU in isolation

The paperclip test tells you whether your PSU can power on by itself, separate from the rest of your PC. This is useful because it narrows down whether the problem is the PSU or something else—like a failed motherboard or a bad power button.

Unplug the PSU from the wall and wait 30 seconds. Locate the 24-pin connector that plugs into your motherboard (the largest cable bundle coming out of the PSU). Find the green wire and the black wire next to it. Straighten a paperclip and insert one end into the connector hole next to the green wire and the other end into the hole next to the black wire. Plug the PSU back in and flip the power switch on the back to ON. The PSU fan should spin. If it does, your PSU is capable of powering on. If nothing happens, the PSU itself is likely dead.

Once the fan spins, unplug the PSU again to stop it. This test does not tell you whether the PSU is delivering the right voltage to your PC—only that it can turn on. If your PC still won't start after the paperclip test shows the PSU works, the problem lies elsewhere.

Watch for signs of power delivery failure

A PSU can turn on but still fail to deliver stable power to your components. The most common sign is random shutdowns or restarts, especially during demanding tasks like gaming or video editing. Your PC may also freeze, display corrupted graphics, or show a blue screen error. These symptoms often point to a PSU that is aging or overloaded.

Check your PC's temperature using free software like HWiNFO or Core Temp. read the program, run it, and look at the CPU and GPU temperatures while your PC is idle. If temperatures are normal (CPU under 50°C, GPU under 60°C at rest) but your PC still shuts down under load, power delivery is the likely culprit. If temperatures are climbing into the 80s or 90s, your cooling system may be the problem instead.

Another clue is the age of your PSU. Most PSUs are rated to last five to seven years under normal use. If yours is older than that and showing any of these signs, replacement is usually the safest choice. Trying to repair a PSU is rarely worth the cost or risk.

Check the power cables and connectors

Loose or damaged cables can prevent power from reaching your components even if the PSU itself is fine. Shut down your PC completely and unplug it from the wall. Open the case and visually inspect every cable connection.

Look for the 24-pin motherboard connector, the 8-pin CPU power connector (usually near the top of the motherboard), and the PCIe power connectors on your graphics card (usually 6-pin or 8-pin). Each connector should be pushed in firmly until you hear or feel a click. If a connector is loose, reseat it by pulling it out gently and pushing it back in until it clicks.

Check for burn marks, melted plastic, or discoloration around any connector. If you see damage, that cable or connector is unsafe and the PSU should be replaced. Also look inside the PSU case itself through any vents—if you see dust buildup, the PSU is not cooling properly and should be cleaned or replaced by a professional.

Measure voltage output with a multimeter (optional but thorough)

If you own a multimeter, you can measure whether your PSU is delivering the correct voltage. This is more technical than the other checks, but it gives you concrete data. Set your multimeter to DC voltage mode and turn on your PC.

Locate a spare Molex connector (the older four-pin power connector) or SATA power connector that is not plugged into anything. Carefully touch the multimeter probes to the pins: red probe to the positive (usually red or yellow wire) and black probe to ground (usually black wire). A healthy PSU should read close to the rated voltage—12V for red wires, 5V for yellow wires, 3.3V for orange wires. Readings that are more than 10% off (so below 10.8V or above 13.2V for the 12V rail) suggest the PSU is failing.

If you are not comfortable working inside your PC or using a multimeter, skip this step. The other checks will tell you what you need to know.

When to replace versus troubleshoot further

If the paperclip test shows your PSU powers on but your PC still will not start, the problem is likely not the PSU. Try reseating your RAM and graphics card, check that all cables are connected, and make sure your monitor is plugged into the graphics card (not the motherboard). If the PC still does not start, you may need to consult a technician or post details on a PC building forum.

If the paperclip test fails and nothing happens, your PSU is dead and needs replacement. If your PSU passes the paperclip test but your PC shuts down randomly, shows corrupted graphics, or fails to boot under load, the PSU is likely failing and replacement is the practical choice. PSU repair is rarely offered by manufacturers and is not worth the cost or downtime.

When you replace your PSU, choose one with a wattage rating at least 20% higher than your system's peak draw. A PC with a high-end graphics card and CPU might need 750W; a basic office PC might need 450W. Check your current PSU's label for its rated wattage, and look up your graphics card and CPU power requirements online to estimate your system's needs.

Frequently Asked Questions

What does it mean if my PSU fan never spins?

Most modern PSUs only spin the fan when the system is under load or when temperatures rise. A PSU fan that never spins at all, even during the paperclip test or when your PC is working hard, suggests the fan motor is dead or the PSU is not powering on. Try the paperclip test to confirm the PSU can turn on. If it does not, the PSU needs replacement.

Can a PSU fail partially and still work sometimes?

Yes. A failing PSU may work fine for weeks, then suddenly shut your PC down or cause random errors. This happens because internal components degrade over time. Once a PSU starts showing these signs, it will usually get worse. Replacement is safer than waiting for complete failure.

Is it safe to use my PC if the PSU feels warm?

PSUs naturally get warm during use. If the case is warm to the touch but not hot, that is normal. If it is too hot to hold your hand on it for more than a few seconds, or if you smell burning plastic, unplug the PC when ready. Do not use it again until the PSU is replaced.

How do I know if my PSU is strong enough for my PC?

Check the label on your current PSU for its wattage rating. Look up the power requirements of your graphics card and CPU online and add them together, then add 100W for the rest of your system. Your PSU should be rated at least 20% higher than that total. If it is not, your PSU may be working too hard and failing prematurely.

What should I do with an old PSU after I replace it?

Do not throw it in the trash. PSUs contain capacitors and other components that should not go to a landfill. Take it to an electronics recycling center, a computer repair shop that accepts old parts, or check whether your local waste management facility has an e-waste collection day.