Every other page in this series says test before you buy. This page says the opposite: a burning smell is the one diagnosis you make with your nose — and the correct next step is the plug, not a multimeter.
Most PC faults invite investigation. This one forbids it. A burning, chemical or hot-plastic smell means something inside has already overheated past its limits — most often a component cooking inside the SMPS. Power supplies store real energy, and a unit that is cooking can move from smell to smoke. The order here is short, and it starts with stopping, not measuring.
The power supply is where the PC's energy concentrates. Inside it, failed capacitors vent hot chemical vapour, overheated windings cook their insulation, and dust blankets cook on hot components for weeks before the smell escapes. That sweet-chemical or burnt-plastic odour near the rear exhaust of the cabinet is the signature.
Other parts can smell too — a dying fan bearing, a burnt drive board — but the SMPS is the most common source and the only one holding dangerous stored energy. Treat the smell as the supply's until the machine is safely open and unplugged — and even then, you inspect the unit from outside only.
If you ever see actual smoke or flame, the rule grows: plug out, no water anywhere near it, and treat it as the electrical incident it is.
Once cold and unplugged, you may look — from outside the sealed box. A bulging or discoloured top cover (swollen capacitors pushing from inside), scorch marks around the fan grill, a melted or browned power socket, and a smell that is strongest at the SMPS exhaust all close the case.
Check the rest of the cabinet too, from a safe distance: dust blankets on the unit's vents explain the cooking and warn you about the replacement's future. Photograph what you find — it helps with any warranty claim and with the technician if you use one.
Every test in this series — paperclip, multimeter, swap — assumes a unit that is safe to run. A unit that smells burnt has left that category. Running it again to 'confirm' risks the motherboard, the drives and the room, to prove something your nose has already proven.
And the one inspection that could add detail — opening the box — is the one thing never to do: capacitors inside hold a dangerous charge long after unplugging. The unit is a sealed, replace-only part. Burnt smell equals replacement. There is no next test.
If the drives or motherboard misbehave afterwards, check them promptly — a cooking supply sometimes takes company with it, which the last page of this series covers.
The video covers the full SMPS checking method for ordinary faults — for this one symptom, the only step that matters is on this page: stop, unplug, replace.
▶️ Watch Full VideoNo. A faint smell is an early smell, not a safe one — it means something has started cooking and will not un-cook itself. Every extra hour under power deepens the damage and raises the risk to the rest of the PC. Unplug it, inspect from outside, and arrange the replacement while the machine still has healthy parts worth protecting.
A brand-new unit can give off a mild warm-electronics odour for its first hours — that is light, fades quickly, and comes with no other symptom. A burning, chemical or hot-plastic smell, a smell that is growing, or one that arrives months into the unit's life is a different thing entirely. When in doubt, treat it as the fault: stopping costs you an hour; being wrong the other way can cost the PC.
Never with a burnt-smelling unit — that is the whole point of this page. If you want certainty before spending, use the opposite test: borrow a known-good SMPS and run the PC on it. If the PC runs clean and cool on the borrowed unit, you have your confirmation without ever powering the suspect again.