"You're not using it right........."
Slightly more recently than this story, in the days when the UK mains voltage had not harmonised with Europe, so was still 240 V (later to become a nominal 220 V).
As a tech person, I worked in a non-tech department of a well-known university. Being the most computerised of the groups in the department, we had bought two UPS to support a small UNIX cluster.
After a few years, as more groups acquired more mains-powered devices, come around 11 am when the kettles went on, the UPS switch in and start beeping, but mains feed is still "live". We check with the manual. which states that trip is set at 209 V.
I found a consumer socket in the room close to the incoming feeder: yup 240 V, but 3 floors up 208 V (My reading of the then-applicable wiring regs allowed for maximum 8% voltage drop in feeders).
I sent a report to a committee to suggest we needed re-wiring, and soon. Report rejected.
Feedback received along the lines of "This person does not know how to use a UPS".
It took a few more years before it was re-wired, in the meantime we had a regular alarm clock for the morning break. UPS capacity was sufficient to cover the surge.