In this guide (8 sections)
The power supplyPSU (power supply): The power supply: the box that takes power from the wall and feeds every part through cables. More in our PC basics glossary → turns the electricity from the wall into the power every part of the PC uses. When it starts to fail, the symptoms can look like almost anything else: shutdowns, restarts, a PC that won’t start. A few signs point to it clearly, and you can test it safely without ever opening it.
Quick fix
The short version:
- Burning smell, smoke or a loud pop? Switch off at the wall and don’t use the PC until the power supply is replaced. See what it means.
- Note what happens: instant shutdowns, needing to flip the power supply switch, or no power at all are the classic signs. The signs.
- Test it: the surest test is swapping in a known-good power supply. How to test.
- Check its age and warranty: many power supplies have 5–10 year warranties. Why it matters.
Want to see what others found? Read 3 real cases from PC forums.
The warning signs
| What you notice | How strongly it points to the power supply | Where to look |
|---|---|---|
| You notice a burning smell, smoke or a pop. | Very strong: stop using it | Sign 1 |
| The PC won’t start until you flip the power supply switch off and on. | Strong | Sign 2 |
| The PC shuts down instantly, especially in games. | Strong, but heat and cables can cause it too | Sign 3 |
| The PC restarts by itself or shows blue screens. | Weak: usually software or RAM | Sign 3 |
| There’s no power at all: no fans and no lights. | Strong, after checking the cable and switch | Sign 4 |
| You hear clicking, buzzing or grinding from the power supply. | Depends on the noise | Power supply noises |
1. There’s a burning smell, smoke or a pop
A sharp electrical smell, smoke, or a loud pop or bang from the back of the PC means a part inside the power supply has failed.
What to do: switch off at the wall, unplug the PC and don’t turn it on again with that power supply. Never open a power supply: its parts can hold a dangerous charge even when unplugged. A brand-new PC can have a faint “new electronics” smell for the first few hours, but that’s mild and fades; anything sharp, or a smell that appears suddenly, isn’t normal.
2. It only starts again after you switch the power supply off and on
If the PC shuts off and then refuses to turn on until you flip the switch on the back of the power supply (or unplug it for a few seconds), the power supply’s protectionShort-circuit protection (OCP/SCP): Safety features in the power supply that cut the power instantly if something is wired wrong or shorting. More in our Power supplies & cables glossary → has tripped. Something made it think there was a fault.
That “something” is often the power supply itself struggling, but a short circuit or a wrong cable can trigger it too. If nothing in the PC changed recently, the power supply is the prime suspect.
3. It shuts down suddenly under load
A power supply that’s ageing or not good enough may cope on the desktop but switch off when a game makes the graphics card demand more power. The PC goes off instantly, with no error.
Overheating and loose cables cause the same symptom, so check those first: our guide on a PC that turns off while gaming walks through all the causes in order.
Random restarts and blue screens are different: they usually come from Windows, drivers or unstable RAM settings, not the power supply. Our guide on how to find what caused a blue screen shows how to find which.
4. The PC won’t turn on at all
No fans, no lights, nothing when you press the button. Before blaming the power supply:
- Check the switch on the back of the power supply is on (marked “I”) and the cable is pushed in at both ends.
- Try another wall socket, without a power strip.
- Check the case’s power button cable on the motherboard (how to check it).
If all that is fine and the PC is completely dead, especially after a pop or a power cut, the power supply is the most likely cause.
How to test the power supply safely
From most to least reliable:
- Swap in a known-good power supply. Borrow one from a friend or another PC, with enough watts for your parts. If the problem disappears, you’ve found it. This is the test repair shops use.
- A power supply tester. Cheap testers plug into the power supply’s cables and show whether each voltage is present. They can catch a dead unit, but they can’t test it under gaming load.
- The paperclip testPaperclip test: A quick check that a power supply turns on by itself, using a bent paperclip on its 24-pin plug. More in our Power supplies & cables glossary → shows only whether the power supply switches on at all. Note that many modern power supplies keep their fan stopped at low load, so a still fan doesn’t always mean it’s dead.
Software readings of voltages in Windows are often inaccurate, so don’t rely on them alone.
How to check its age and warranty
Power supplies wear out. Parts inside slowly age, especially in hot, dusty cases, and a unit that coped with your PC for years may stop coping with a newer, hungrier graphics card.
- Check the warranty: many good power supplies come with 5, 7, 10 or even 12 years. The serial number label on the side usually shows the date.
- When replacing it, choose a reputable model with enough watts and a long warranty. The 80 Plus rating80 Plus rating (Bronze, Gold, Platinum): A sticker that says how efficient a power supply is. It isn't a measure of quality or reliability. More in our Power supplies & cables glossary → shows efficiency, not quality, so check independent reviews too. Our guide on how many watts you need helps you choose.
Real cases: what other users ran into
These are real reports from PC forums, summarized in our own words, with a link to each original thread.
Real caseCore i7-13700K · Radeon RX 7900 XT · Corsair RM850xSolved by replacing hardwareA pop, and then a completely dead PC
A four-month-old prebuilt made a “pop” when the owner pressed the power button to wake it, and then had no power at all, with no burning smell. A cheap power supply tester showed nothing, and with the paperclip test the power supply’s fan didn’t spin. The owner replaced it with the same model and the PC worked again.
Takeaway: a pop followed by no power is a classic power supply failure, even in a new PC. See warning sign 4.
Source: Tom's Hardware Forum
Real caseRyzen 7 5800X3D · RTX 3070 · Corsair 750 W (5 years old)Solution not confirmed by the userOnly starting again after switching the power supply off and on
The PC switched off instantly, in games, films and even on the desktop, with no blue screen, and wouldn’t start again until the power supply was switched off and on. A clean Windows install didn’t help. Replies explained that this means the power supply’s safety protection is tripping, and advised replacing it first. The owner ordered a new 1000 W unit; the thread doesn’t show the result.
Takeaway: needing to power-cycle the power supply is one of the clearest signs. See warning sign 2.
Source: Tom's Hardware Forum
Real caseNOX Hummer X 650 WSolution not confirmed by the userRandom restarts, then a burning smell after a power cut
A newly built PC started restarting at random. After a power cut in the house, the power supply gave off a burning smell when the owner tried to turn it on. Replies agreed the power supply had failed, advised a warranty claim and warned not to use it again. The owner worried the warranty might not cover it because the house had no earth connection.
Takeaway: a burning smell means stop using it, even if the PC still starts. See warning sign 1.
Source: Tom's Hardware Forum
Frequently asked questions
How long does a power supply last?
A good one often lasts 7–10 years or more; cheap ones can fail much sooner. Heat and dust shorten their life.
Can a failing power supply damage other parts?
It can, though it’s rare with good units, which shut themselves off safely. Cheap units are more likely to take other parts with them, which is why a burning smell or pop means stop immediately.
Can I repair a power supply?
No. Don’t open it: the parts inside can hold a dangerous charge. Replace it, or use the warranty.
Is a higher wattage power supply more reliable?
Not by itself. Quality matters more than wattage: a good 750 W unit is better than a poor 1000 W one.
Do I need to replace the cables too?
On a modular power supply, use only the cables that came with the new unit. Cables from different brands, or even different models, can be wired differently and damage parts.
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