How to Tell if You Have a Failed PSU (Symptoms Indicating You Have a Bad Power Supply)

Modular power supply with cables for desktop pc

How to Tell if You Have a Failed PSU (Symptoms Indicating You Have a Bad Power Supply)

Key Points

  • Power supply units (PSUs) are often overlooked as a potential cause of computer failures, but they can easily be overloaded and fail.
  • Symptoms of a failed PSU include a burning smell or smoke, the PC not turning on or booting, random shutdowns or restarts, blue screens of death, and noise coming from the back of the computer case.
  • To test for a failed PSU, you can check if it is turned on, test the PSU’s cable and wall socket, check internal connections, perform swap testing with a spare computer, or do a paperclip test.
  • Using a multimeter or power supply testers can also be used to test the functionality of a power supply, but they may not be cost-effective compared to simply replacing the PSU.

Electrical components fail. That’s a fact of life and something that every computer technician comes to terms with early on in their career. Power supply units, or PSUs, aren’t usually the first thing we think of when we consider failed components, but they’re surprisingly easy to overload. Testing and identifying a failed PSU is a crucial skill that computer technicians and repair folks need to serve their customers properly. Here are some symptoms of a failed PSU and some tests you can run to test if your power supply is working.

Symptoms of a Failed PSU

A couple of things indicate an apparent failure in your PSU, but most of the components in a computer are far more likely to be the culprit of a computer crash. If you bought a high-quality PSU and haven’t actively begun using components that draw more power than the PSU is rated for, it’s unlikely that your PSU will fail. However, a few symptoms might indicate a problem with your PSU. Let’s take a look at those.

Power rating. Power rating section of a power supply unit. Focus on "Max Current". Shallow depth of field.
Check your PSU rating to ensure your components don’t draw more power than the PSU is rated for.


Burning Smell or Smoke from the PSU

This one should go without saying, but we’ll cover it for completeness. If your PSU starts to smoke or you smell any kind of burning coming from your PSU, your PSU has failed and needs to be replaced. In fact, this may be the only smoking gun for a dead PSU. 

If your PSU starts to smell smoky or actually emit smoke, it’s crucial that you stop using the PSU immediately. While it might be tempting to power through it until your new PSU arrives, using a PSU that is quite literally on fire is dangerous and could damage other parts of your computer.

PC Won’t Boot or Turn On

If the PC won’t turn on or boot, this is a good sign that your PSU has failed. This symptom is another pretty good sign that your PC suffers from PSU issues. However, to diagnose this issue, you’ll need to ensure that your motherboard is equipped with a motherboard speaker. 

If your PC refuses to boot because the PSU is dead, the speaker won’t make any sound. If the PSU is turning on but another dead component causes the PC to refuse to boot, the Power-On Self-Test (POST) code will indicate what component is broken. However, with a dead PSU, no POST can occur.

The POST code you hear will depend on the motherboard’s BIOS vendor. You’ll need to find the POST code list for your specific BIOS. Otherwise, you could misunderstand the POST code and replace the wrong part. Most BIOS vendors have a list of their POST codes available online. You’ll only need to determine who your BIOS vendor is and search for it from a functioning device with an internet connection.

The Computer Randomly Shuts Down or Restarts

Random shutdowns and restarts could be a symptom of a failing PSU. However, it’s crucial to remember that unexpected shutdowns and restarts could also be a symptom of an overheating central processing unit. So, if you’re experiencing random shutdowns and restarts, you’ll want to run some diagnostics on your CPU before you replace your PSU.

First, to test if your CPU is causing your random shutdowns, open the case and clean the dust out of the heatsink. Then run the CPU at a low load while using a CPU monitoring program like Core Temp. If you have an Intel CPU, Core Temp will even tell you the temperature of the individual cores of your CPU! 

Use Core Temp to check your CPU temperature while doing various tasks. A temperature range of 40-60°C (104–140°F) is what you should expect for a normal workload. Intensive tasks like gaming, video editing, or programming may see temperatures of 60–80°C (140-176°F). Anything over 80°C (176°F) could damage the CPU’s cores; it’s overheating if your CPU runs hotter than 85°C (185°F).

Random Blue Screen of Death

Failed PSU
A failing PSU can sometimes cause the Blue Screen of Death on Windows PCs.


While the most common cause of the Blue Screen of Death is faulty RAM sticks, a faulty PSU can cause this as well. If your PSU is causing your computer to experience Blue Screens of Death, a few reasons might be the underlying cause.

Insufficient voltage is the most common problem with PSUs that cause this issue. When the PSU can’t provide sufficient voltage to the computer’s components, they malfunction, and the CPU will call for an immediate shutdown, triggering the Blue Screen of Death.

Noise from the Back of the Computer Case

If your PSU is starting to go, you might hear noise coming from the back of the computer case where the PSU is located. Sounds of a failing PSU include increased fan cycles, noisy fan cycles, clanking and clattering, and a loud humming sound.

However, several parts of a computer can make these noises. It’s crucial to ensure that the component you’re hearing is your PSU. The problem could also be your GPU or CPU fans, which can have noisy cycles or clattering when they’re going bad.

How to Test for a Failed PSU

You should take a few steps to ensure your PSU is functioning correctly. First, you should ensure that the PSU is actually turned on. Power supplies have an external power switch on the back that can get bumped and turned off. So, ensure the switch is turned to the “On” position.

Then, you’ll want to ensure the PSU’s cable is stably input and functional. You’ll need a second cable that fits your PSU to test this. Plug in the second cable and see if the PSU turns on with the new cable. If the other cable was functioning in a different computer, but doesn’t function in the broken computer, then the PSU is probably bad.

You’ll also want to check with a different wall socket to ensure that the wall socket hasn’t blown out. If the wall socket is blown, you might need to replace it. However, it could also be a breaker flip. So, check the breakers, then see if the wall socket needs to be repaired by trying the computer in a different wall socket.

Now, you’ll want to check the internal connections between the power supply and the components. Ensure that the power supply connections to the motherboard, GPU, and hard drives are all secure and none of the pins are bent or broken.

Remove all components besides the CPU, RAM, and boot drive if all connections are secure. If your CPU has on-board graphics, remove the GPU. If the CPU does not have on-board graphics, leave the GPU plugged in. See if you can boot your computer with fewer components plugged in.

Swap Testing

If you have a spare computer lying around, you can swap-test your PSU by plugging it into the spare PC. You can also swap that PC’s PSU into your original PC to see if you can boot the original PC with a different PSU.

Power supply cable connecting to computer
Plug your PSU into a spare computer to see if that computer will power up.

©Sunshine Studio/Shutterstock.com

Paperclip Test

If you’re feeling extra feisty, you can do a paperclip test to see if the PSU is functioning. To do a paperclip test, start by powering your computer down and unplugging all plugs from the PSU except for the AC adapter and the 24-pin cable.

Take the 24-pin cable and locate the 16th and 17th pins. To find these pins, hold the clip facing upwards with the pins facing toward you. The 16th and 17th pins are the 4th and 5th pins on the top, counting from the left to the right.

Take a paperclip and insert each end of the paperclip into the 16th and 17th pins. Then power on the power supply. If the PSU’s fan turns on, the PSU is functioning normally. 

It’s worth noting that some PSUs have a zero-RPM function that will cause the fan to spin a few times and then stop. The PSU still functions normally if the fan stops after spinning for a short while.

Should I Test My Power Supply with a Multimeter?

A multimeter can be used to test the functionality of a power supply. Although the low cost of power supplies compared to a multimeter makes it typically less efficient to buy the multimeter. Unless, of course, you’re a business that repairs computers.

Similarly, power supply testers can be used to test the functionality of a power supply. However, they typically cost more than just replacing the power supply outright. So, if your PSU didn’t pass the paperclip and swap tests, you’re probably better off just buying a new power supply.

Summary Table

Symptoms of a Failed PSUHow to Test for a Failed PSU
Burning Smell or Smoke from the PSUEnsure the PSU is turned on
PC Won’t Boot or Turn OnCheck the PSU’s cable
The Computer Randomly Shuts Down or RestartsTry a different wall socket
Random Blue Screen of DeathCheck the internal connections
Noise from the Back of the Computer CaseRemove all components besides the CPU, RAM, and boot drive
Swap Testing
Paperclip Test

Frequently Asked Questions

What is a power supply unit?

A power supply unit is a core component of a modern computer that converts alternating current voltage (AC) into direct current (DC). It manages the voltage output to the components to ensure that the voltages are fine-tuned to the needs of a modern computer.

What is the difference between a modular and a non-modular PSU?

A modular PSU has connections for the different types of cables that connect to computer components. A non-modular PSU has all the cables hard-wired into the PSU.

What are the signs of a failed PSU?

The most common sign of a failed PSU is unexpected shutdowns or restarts. However, some computers with failed PSUs may experience Blue Screens of Death, excessive noise from the back of the case, and even smoking or burning smells from the PSU.

How can I test my PSU?

The most reliable way to test a PSU is a swap test, where you try the PSU with a different machine. However, if you don’t have a separate machine to test with, a paperclip test can determine whether your PSU is functioning.

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