how to test PC PSU

How To Test PC PSU? A Comprehensive Guide

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Reliable power is crucial for any personal computer system. The power supply unit, commonly referred to as the PSU is responsible for taking incoming electricity from the wall outlet and converting it into the precise voltages needed to run all of the components inside the PC case. It powers everything from the CPU and graphics card to storage devices and cooling fans. Given how critical the PSU is, it’s important to routinely evaluate its health and performance to ensure it continues functioning properly over time. An inefficient or failing PSU can cause a host of issues for other parts and even lead to system instability or damage under the worst circumstances. In this blog post, we will explore several methods for how to test PC PSU. We will cover both simple and advanced diagnostic techniques to analyze critical voltage outputs and load-handling capabilities.

Understanding the Basics of a PSU:

The PC power supply unit, or PSU, is responsible for taking the 120-240 volt alternating current (AC) from a wall outlet and converting it to stable, regulated direct current (DC) voltages that all the components inside the computer require. Modern PSUs produce +3.3V, +5V, +12V, and -12V power rails that are distributed via 20/24-pin and 4/6-pin peripheral connectors. Higher wattage PSUs are needed to power beefier systems with multiple graphics cards and overclocked processors. The efficiency rating also affects overall power usage and heat generation. Ensuring your PSU matches or exceeds the rated needs of your components is key.

Importance of Testing Your PSU

It is critically important to routinely test your PC’s power supply unit. As the central component distributing power to all other parts, a faulty or degraded PSU can cause a host of unpredictable issues. It may lead to crashes, unexpected reboots, instability when overclocking, or even damage to other hardware over time. By testing voltages, functionality, and load handling ability, you can catch small problems before they worsen. This gives you time to replace the PSU if needed and avoid potentially expensive damage to other components down the road. Testing is a quick, non-invasive way to check the PSU’s health and gives valuable insight into potential upgrading needs.

Signs of a Faulty PSU:

Before proceeding with testing, it’s essential to be aware of the signs that may indicate a faulty PSU:

  • Random reboots/crashes – If the computer unexpectedly turns off or reboots for no apparent reason, it could be a sign the PSU is unstable and failing to provide clean power.
  • Components not powering on – Individual parts like the graphics card, storage drives or case fans may not spin up during boot, indicating insufficient power from the PSU.
  • Blue screens/errors – PSU issues can cause BSoDs (blue screens of death) or kernel power errors in Windows.
  • Buzzing/humming noises – Abnormal sounds coming from the PSU, especially the fan, means something isn’t right internally.
  • Smelling burned components – A distinct “electrical fire” smell suggests overheating inside the PSU from a short or malfunction.
  • Voltage instability – Using a multimeter shows the +12V rail is inconsistently below or above the acceptable range.
  • Inability to power new components – An underpowered PSU may work now but cannot handle additional upgrades.
  • Bad power connections – Loose, damaged or corroded peripheral power cables affect power delivery.
  • Caps leaking/bulging – Leaking or bulging electrolytic capacitors need replacement.
  • Failing fan – An erratic, loud or dying PSU cooling fan needs attention.

Precautions Before Testing:

Before testing your PSU, it’s crucial to take some precautions to ensure your safety and prevent damage to your hardware:

  • Power off your computer and disconnect it from the electrical outlet.
  • Wait for a few minutes to allow the capacitors to discharge completely.
  • Use an anti-static wrist strap to prevent static discharge, especially if you’re handling sensitive components.
  • Handle the PSU and testing equipment with care to avoid electrical shocks.

How To Test PC PSU?

Using a Power Supply Tester:

One of the simplest methods for testing a PSU is using a dedicated power supply tester. These testers come in various forms, from basic LED indicators to more advanced models with digital readouts. Here’s how to use a power supply tester:

  • Disconnect the PSU from your computer and all other components.
  • Plug the main 24-pin or 20+4-pin connector from the PSU into the corresponding slot on the tester.
  • Connect any additional power cables (CPU, GPU, SATA, etc.) to the appropriate slots on the tester.
  • Power on the PSU using the switch on the back or by momentarily connecting the green wire to any black wire on the 24-pin connector using a paperclip.
  • Observe the LED indicators or digital readout on the tester. They should indicate whether each voltage rail (3.3V, 5V, 12V) is within acceptable ranges.
  • If the tester indicates any abnormalities or if the PSU fails to power on, it may be faulty and require replacement.

Using a Multimeter To Test PC PSU:

Alternatively, you can use a multimeter to test the output voltages of your PSU manually. Here’s how to do it:

  • Set your multimeter to DC voltage mode and ensure it’s capable of measuring at least 20 volts.
  • Disconnect the PSU from your computer and all other components.
  • Locate the main 24-pin or 20+4-pin connector from the PSU.
  • Turn on your PSU using the switch on the back or by momentarily connecting the green wire to any black wire on the 24-pin connector using a paperclip.
  • Place the black probe (negative) of your multimeter on any black wire (ground) and the red probe (positive) on the corresponding coloured wires to measure their voltages.
  • Refer to your PSU’s specifications to determine the acceptable voltage ranges for each rail (3.3V, 5V, 12V). Ensure that the measured voltages fall within these ranges.
  • If any voltage readings are significantly outside the acceptable ranges, it may indicate a faulty PSU.

Paperclip Test (Not Recommended for Novices):

The paperclip test is a rudimentary method for quickly determining whether a PSU powers on, but it does not provide information about the output voltages. Here’s how to perform the paperclip test:

  • Disconnect the PSU from your computer and all other components.
  • Locate the main 24-pin or 20+4-pin connector from the PSU.
  • Bend a paperclip into a U-shape and insert one end into the green wire (PSU_ON) pin and the other end into any black wire (ground) pin on the 24-pin connector.
  • Turn on your PSU using the switch on the back.
  • If the PSU’s fan spins up and any attached peripherals receive power, it indicates that the PSU is capable of turning on. However, this does not guarantee that it’s functioning correctly or providing stable power.

Observing for Visual Signs:

In some cases, visual inspection of the PSU can provide clues about its health. Look for the following signs:

  • Bulging or leaking capacitors.
  • Burn marks or discolouration on the PCB.
  • Unusual smells or noises coming from the PSU.
  • Excessive dust buildup, which can obstruct airflow and cause overheating.

Replacing the PSU:

If your testing determines the PSU is faulty or failing, it’s important to replace it promptly. A failing PSU not only can cause system instability and crashes, but prolonged use may damage other components. When replacing the PSU, choose a new unit that provides sufficient power for your system. Look at the wattage requirements for your graphics card, CPU and other hardware to ensure the replacement PSU meets or exceeds the total wattage needed.

Ensure the new PSU connector types match your motherboard and devices. Then, power down the system and unplug the power cable. Open your PC case and carefully disconnect all cables from the old PSU, taking note of their positions. Remove any screws securing the PSU if necessary. Install the new PSU into the case in the same orientation and route all cables to their proper positions. Replace any screws and power the system on to verify proper functionality.

Tips For the Longevity of PSU:

Here are some tips to help maximize the longevity of your PC power supply unit:

  • Provide adequate ventilation – Ensure the PSU isn’t obstructed and has ample airflow to dissipate heat. Good case cooling is important.
  • Use a surge protector – A surge protector can shield the PSU from power spikes that may damage components over time.
  • Clean periodically – Use compressed air to blow out dust buildup from the PSU fan and heatsinks.
  • Proper wattage – Don’t overload the PSU. Give it some headroom over what your estimated power needs are.
  • Moderate load – Running the PSU near its limit for prolonged periods puts strain on it.
  • Replace old cables – After several years, wiring can degrade and become a fire risk.
  • Monitor voltages – Signs of ageing include voltage fluctuations outside specs.
  • De-clutter inside case – Organize cables to allow airflow and avoid kinking.
  • Firm connections – Wiggle components to check all power connections are secure.
  • PSU location – Intake/exhaust should be unobstructed and away from hot components.
  • Avoid movement – Don’t move your PC with the power cable connected.
  • Annual checkup – Check voltages once a year to catch issues early. Replace if over 5 years.


In summary of how to test PC PSU, regular testing of your PC’s power supply unit is an important maintenance task to ensure reliable, stable system performance over the long run. A faulty or overworked PSU can cause significant issues. The various testing methods covered in this article, such as the paperclip test, multimeter voltage checking, and load testing, allow you to thoroughly evaluate the functional and safety aspects of the PSU. Being proactive in monitoring your PSU health through simple tests like these could potentially prevent unnecessary downtime, crashes, and even costly damage to other components. Replacing the PSU when test results show declining quality or inability to handle modern demands is also recommended. With proper testing and maintenance, your PSU can power your PC system efficiently for many years to come.

FAQs About How To Test PC PSU:

Q. How do I safely disconnect my PSU?

A. Ensure your computer is off, unplug from the wall, and wait for capacitors to discharge before disconnecting cables.

Q. Can I test a PSU without removing it?

A. Yes, using a power supply tester or multimeter doesn’t require removing the PSU from your computer case.

Q. What if my PSU passes the test but my PC still won’t turn on?

A. Check other components like the motherboard, CPU, and RAM for issues that may prevent booting.

Q. Is it normal for a PSU to make noise?

A. Minimal noise from the PSU fan is normal, but any loud buzzing or clicking sounds could indicate a problem.

Q. Can I test a PSU without a load?

A. Yes, but keep in mind that a load test with components connected may provide a more accurate assessment of PSU health.

Last Updated on 4 June 2024 by Ansa Imran

Haleema is an experienced PC builder

Haleema is an experienced PC builder who has been building PCs for the last couple of years. He has written several articles on PC components, including power supplies and graphics cards. In his articles, he explains how to check the compatibility of a power supply with a GPU and what things to consider when pairing them.

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