"Not
sure what went pop though, nothing obvious".
Most electrolytic caps have a
safety vent on their bottom. You will hear it blow, but
there will usually be no visible signs on the PCB top side, other
than possibly some expulsed electrolyte around the cap's sides.
"I was
quite surprised how much dust was inside the PSU which certainly
wouldn't have helped it's lifespan".
Hence, my mentioning the "dust
bunny margin".
"And
unlike the inside of the computer it's not something that can be
removed easily with the little warranty stickers they put on the
screws".
Which is why I either ignore those stickers
(as more than a year is really too long to wait) or put a sticky note,
having the warranty expiry date on the case's outside, reminding me
to do a cleaning as soon as possible thereafter.
It also helps if you have a case that has a
removable filter on the air-intake, like some Lian-Li models.