I started using a Tagan 700BZ PSU in my computer a couple of months ago - my first PSU with active PFC. The UPS is a basic one that has served me well for 10 years, and outputs a square wave on battery. While setting up this particular combination, I briefly wondered how the PFC circuit would react to working with non-sinusoidal power but then forgot about it - until it died a couple of days ago. It blew the fuse on the UPS and shows a short at the AC input. One of the two paralleled 20N60C3 MOSFETs was a dead short.
The UPS battery - a 70Ah car battery - is of the same age as the UPS (10 yrs) and has little backup power left. So I always shut my computer down quickly in the event of a power outage, of which there were dozens during the 2 months I've been using this PSU.
The PSU died while I was in another room. I didn't notice a power outage or fluctuation during that time but can't be 100% certain. Is it likely that there was an outage and the PFC transistor was finally killed by the square-wave supply?
To put it another way, if I repair the PSU, is it likely to go poof again unless I change my UPS to a more sophisticated one? I'd never done a detailed study of practical active PFCs before and could well miss something with a quick analysis.
(I did some online reading about active PFCs and non-sinusoidal supplies after my PSU died but they're mostly end-user discussions and are all inconclusive).