A PC supply died with a crack and a smell. The machine went dark mid-task, nothing on the power button, no fans, no click. Dead ATX supplies usually get thrown straight in the bin, and most of the time that is the right call. But this one was a decent unit and I wanted to know what actually killed it, so I opened it up.
A word before anything else: the big primary-side capacitors in a power supply hold a mains-voltage charge long after you unplug it. They will hurt you. I discharged them through a resistor and checked with a meter before my fingers went anywhere near the board. Treat a PSU like it is live until you have proven otherwise.
The fuse was the obvious clue: blown, blackened glass. But a fuse does not blow for fun. It is the symptom, never the cause, and if you just replace it the new one blows in the same instant. So I went looking for what made it die. The usual suspects in this kind of failure are the primary switching transistors and the bridge rectifier. I put the meter across the rectifier and got a dead short, exactly what I expected: a failed diode shorts the mains straight through and the fuse does its job sacrificing itself to save the rest.
So: a new bridge rectifier, a new fuse, and a careful check of the switching transistors and the gate resistors around them to make sure the failure had not taken anything else with it. It had not. Reassembled, fuse in, and rather than trust it with my actual computer I bridged the green wire to ground on the bench to spin it up on its own. Fans turned, the rails read clean on the meter. Then, and only then, did it go back in a machine.
Two new components, both costing pennies, against a supply that does its job perfectly well. I am not pretending everyone should be poking around inside mains electronics, and I would not do it on the dinner table. But the throwaway culture around PC parts annoys me, and so much of it is one cheap component sitting between a working unit and the skip. Find the real fault, respect the voltage, and a surprising amount of dead kit simply is not.