It would have to have been a surge-protecting power strip? Probably, the MOV's in the surge protector part were interacting with the input circuitry in the UPS. (That alone smacks of bad design, but it's not a huge deal in practice because the UPS usually has surge suppression built in, so why the need to add another one, right? Still, I'm curious if a better-designed surge protector like the Tripp-Lite one would trigger UPS failures. Possibly not.)

OTOH, a simple non-surge power strip with just a switch and outlet taps should surely be OK, shouldn't it? I mean, it's basically just a multi-tap extension cord with a switch... wires and plugs, and no other circuitry.

yes it was a surge-protecting strip, not a basic one. i guess you were talking about a generic power strip? i would expect a generic strip to act like an extension cord and not mess with the UPS. it may also be APC's design - i've never really used tripp-lite but i suspect it's like a dell workstation vs. an ADK or studiocat DAW - one is adequate, the other is professional-grade.

Interesting analogy, Mr. Jack!

my friends said that APC and Tripe Lite are both good brands of UPS. For good spike suppression, I haven't used a UPS before and have two bestek surge protectors. But I'm going to get a UPS for my new home theater this time to protect my expensive devices from damages. For my PC and other mobile electronics, I still use my two surge protectors.