UPSs, in my experience, quite often have or develop faults that defeat their purpose. We just threw one out that would cut power entirely during self-test, but

UPSs, in my experience, quite often have or develop faults that defeat their purpose. We just threw one out that would cut power entirely during self-test, but only during self-test, not during an actual outage. I've seen their battery monitoring circuits fail such that they report a battery as good until power is cut and then die immediately. The other way also happens, reporting all batteries as bad even though they might be brand new, so you're never sure when to replace them. I've come to the conclusion that if you are going to use a UPS, your equipment should always be plugged in to at least 2 UPSs, either via redundant power supplies or an ATS PDU.