Re: leavetaking
Okay, it wasn't the power cord; I'm currently running a new power supply with the same old power cord (because it's a PITA to crawl under my desk to thread a new one to the UPS).
And for future reference, the only practical difference between a 500W and 700W power supply is number of 12V accessory connectors. Each one of those connectors has the same current limit, so if you haven't upgraded your motherboard, video card, or case fan (that runs on direct power supply connection, unlike mine that piggybacks on an old school hard disk power connector), there's nothing gained by going to a higher rated power supply vs. the old one (if it failed, it was probably just component aging or power condition related component damage -- in my case, the dead one had run almost continuously for about six years since my last hardware rebuild, three or four of those years before I got a UPS).
Anyway, the machine is back up; after installing the power supply I had to rerun the Kubuntu 22.04 installer (three times, as it turned out; something damaged my boot loader, then Boot Repair erased a bunch of stuff so I reinstalled to be sure I wasn't missing anything critical, and both of those times I had the wrong username so my old desktop settings and such weren't picked up).
But now I have everything working, my SeaMonkey bookmarks were preserved (meaning that config file, at least, wasn't harmed), and I've gotten critical items reinstalled. I'll probably be finding and reinstalling third party software I need for the next several weeks, depending how frequently I use a particular package, but the core is done.