My BX750MI-GR has saved my precious data on two occasions. Earlier this year, my seven year old, well used waffle iron shorted, popping loudly and sparking quite brightly in the process, probably because of all the gunk that had accumulated inside its less cleanable interior over the years. That not only made my breaker trip, but also blew the 16 amp main fuse. The UPS kicked in immediately, making a klick and a beep, which felt amazing. That was my first time ever.
As for the second time, see this post.
Sounds like knob and tube in the walls. Old code terrifies me. Live-front-end switching and the like. There’s a victorian manor house near me that featured on Tom Scott and talked about having to light lamps with a bath of electrified mercury.