My bench supply started doing that thing where the output sags under any real load and the fan spins up like it's trying to leave. The honest move, by most accounts, is to bin it and buy a replacement. I had a look first.
Popped the lid and there it was: one of the primary-side filter capacitors with a domed top, the classic little plus-sign vent bulging out. The rest of the board looked fine, no scorching, no smell of regret. So this wasn't a mystery, it was a single tired electrolytic that had spent a decade getting warm.
I matched the value and voltage rating, ordered a low-ESR replacement for about five pounds including the postage, and spent twenty minutes with the iron and a bit of solder wick. Discharged the big caps first, because I'm fond of my heartbeat. Reflowed the joints, checked there were no bridges, buttoned it back up.
It works. Output is steady under load again and the fan has calmed down. I'm not pretending this is heroic engineering. But there's something quietly satisfying about a fault that points straight at itself and a fix that costs less than a coffee, against a perfectly good box of transformer and metalwork that was one component away from the skip.