Your PC’s power supply unit (PSU) is like the heart of your computer. It pumps electricity to all the parts — your motherboard, graphics card (GPU), hard drives, and fans. If it doesn’t work right, nothing else will either.
When a PSU starts to fail, your computer might suddenly shut off, fail to turn on, or show other strange problems. A bad PSU can even damage expensive parts of your computer. That’s why it’s important to know how to check if your power supply is working properly.
In this guide, we’ll explain — in simple steps — how to test your computer’s power supply, recognize when it might be failing, and what you can do to fix the issue.
Let’s get started.
Why the Power Supply Matters
Before we look at how to fix PSU problems, let’s understand what it actually does.
The PSU takes power from your wall outlet (AC electricity) and converts it into the lower voltage (DC electricity) your computer needs. It sends the correct amount of voltage to each part of your system.
If the power supply isn’t working correctly, the PC may:
- Not start at all
- Turn off randomly
- Freeze under high load (like while gaming)
- Cause your computer to act weird in general
These issues often look like they’re caused by something else, like a bad motherboard or graphics card. That’s why the PSU can be a sneaky issue to diagnose.
Common Signs Your Power Supply Might Be Failing
Here are some warning signs to look out for — these are your first clues that your power supply might be the problem.
- 🔌 Random Reboots or Shutdowns
Your computer suddenly turns off or restarts by itself — especially while gaming or doing heavy tasks. - ⚠️ Won’t Start or Boots Sometimes
Your PC powers on one day, but refuses the next. That could be a sign your PSU can’t deliver enough startup power. - 💨 Weird Noises from Case
Clicking or high-pitched whining sounds from inside your computer can come from a failing PSU. - 🔎 Burning Smell or Smoke
If you smell something like burning wires or see burnt parts, turn off your PC immediately. Your PSU may be damaged. - 💡 Fans or Lights Not Working
If your case fans, lights, or hard drives suddenly stop working, your PSU may not be sending enough power. - 🌡️ Overheating
If your PC gets very hot or the PSU fan doesn’t spin, that’s a red flag. Bad power can cause components to overheat.
If you notice any of these problems, don’t ignore them. Testing your power supply is the next smart step.
How to Test a PC Power Supply: Step-by-Step Guide
Let’s go over a few safe and easy ways to test your PSU and find out if it’s working properly.
🛠 Note: Always turn off and unplug your computer before touching anything inside.
1. Use a PSU Tester (Easiest & Safest)
A PSU tester is a small, affordable device made just for testing power supplies. It’s easy to use and gives you clear results.
Here’s how to use it:
- Turn off your PC and unplug it from the wall.
- Disconnect all cables going from the PSU to your computer parts.
- Plug the 24-pin connector from the PSU into the tester.
- Turn the power supply back on.
- The tester will display voltages for different outputs — like +12V, +5V, and +3.3V.
Here are the normal ranges:
- +12V: Between 11.4V and 12.6V
- +5V: Between 4.75V and 5.25V
- +3.3V: Between 3.14V and 3.47V
💡 Pro Tip: Many PSU testers will beep or flash a warning if something is out of range.
If the numbers are too high or too low, it’s likely your PSU is failing.
👍 Best for: Beginners, regular PC users, PC builders
2. Do the Paperclip Test (Advanced, Use With Caution)
If you don’t have a PSU tester, you can use a paperclip to find out if the PSU can power on.
⚠️ Caution: This test only checks if the PSU turns on — not if it works properly under load or gives correct voltages.
How to do the paperclip test:
- Unplug the PSU and switch it off.
- Find the big 24-pin power plug.
- Straighten a paperclip and bend it into a U-shape.
- Insert one end of the paperclip into the green wire pin.
- Insert the other end into any black wire pin (ground).
- Plug the PSU back into the wall and switch it on.
If the fan in the PSU turns on, the unit is getting power. If it doesn’t, the PSU is probably dead.
👍 Best for: Tech-savvy users, no tools available
📌 Important: Even if the fan turns on, this test doesn’t confirm that the PSU is delivering the right voltage.
3. Use a Multimeter (More Advanced)
A multimeter is a tool that shows exact voltage output. This method is more involved but gives useful info.
How to test with a multimeter:
- Unplug the PSU from the motherboard and other parts.
- Plug in and turn on the PSU.
- Put the multimeter’s black probe into any black (ground) pin.
- Put the red probe into the pins for +12V, +5V, and +3.3V.
- Compare the readings to the normal ranges:
- +12V: 11.4V – 12.6V
- +5V: 4.75V – 5.25V
- +3.3V: 3.14V – 3.47V
If any reading is far off, your PSU needs replacing.
👍 Best for: Experienced users, IT pros, repair techs
4. Use a Known Working PSU
If you’re still not sure, try using another PSU that you know works.
- Disconnect your current PSU from everything.
- Plug in another PSU to your motherboard and main components.
- Turn on your PC.
If it powers on and works fine now, your old PSU is likely the problem.
👍 Best for: Anyone with access to a spare PSU
How to Check Power Supply on PC Without Tools
Don’t have testers, multimeters, or paperclips? You can still look for clues using software.
Here’s what to try:
- Check for BSOD (blue screen) errors related to power or voltage.
- Use free programs like HWMonitor or Open Hardware Monitor.
- Look inside your BIOS (press Delete or F2 on startup) and check voltages under “PC Health” or “Monitor.”
If the +12V drops close to 11.0V or lower when under load (like while gaming), your PSU might be failing.
👍 Best for: Beginners who want to look for quick signs
When to Replace Your PSU
Sometimes testing confirms what you already suspect: your PSU just isn’t reliable anymore.
Consider replacing your PSU if:
- Voltage readings are out of safe range
- You smell burning plastic or see damage
- Your PSU is making loud or strange noises
- Your PC keeps acting weird unless you use another PSU
⚠️ Warning: A weak or failing PSU can damage your computer parts, especially the motherboard and GPU. Don’t wait too long!
Choosing a Reliable PSU Replacement
If you need a new power supply, make sure to get one that’s safe and well-made.
Look for these features:
- 80 PLUS certification (Bronze, Silver, Gold, or higher)
- Good brand names like Corsair, Seasonic, EVGA, or be quiet!
- Enough wattage for your system (use online PSU calculators)
- Modular cables (for easier cable management and airflow)
Avoid cheap, no-name PSUs. Saving a few dollars isn’t worth risking your whole computer.
🔌 Pro Tip: If you plan to upgrade your graphics card later, get a PSU with a little more wattage than you currently need.
Final Thoughts
Learning how to test a PC power supply is an important skill — even if you’re not a computer expert. A faulty PSU can make your life very frustrating, but if you know what to look for, you can fix the problem before it gets worse.
Next time your PC randomly shuts down or refuses to turn on, ask yourself one question:
Could it be the power supply?
Whether you use a tester, multimeter, or software check, finding PSU issues early can save you from expensive damage later.
✅ Take Action:
Don’t wait for disaster. Buy a basic PSU tester or add power supply testing to your regular PC check-up every 6 months. It’s fast, easy, and could save your system.