Ditto. I have a surge protector but never turn off my mac-mini. That said, I have a laptop that I turn off when not in use. I’ve seen enough battery failures in older laptops to suggest that I should disconnect it from the power grid when not in use.
That was an unwritten rule even back in the DOS days. It was healthier for the PC to stay on rather than turn it off every day.
zeugma, I tried to reach the end (to make sure it wasn’t already stated) before I mentioned this, but another possibility is that you may have too much plugged into the UPS.
Also, if you have a laser printer connected, that could be the issue too. Laser printers are a no-no for a UPS because they use a power surge to use the fuser (the thing it melts the toner to the paper).
All the other assistance here on this thread have probably already covered your problem, but I thought I would throw this in too.