Faulty iron in another room fried my LaserJet. UPS isn't just for loss of power, it should also protect from power spikes. Btw. printer was connected to a (cheap) surge protector strip which didn't help. On positive side nothing else was fried and laser was fixed for 40 euros.
Is it ironic that the electrically expensive part of the LaserJet, the fused, is pretty much an iron in a different format?
It's not connected to the UPS directly, it's causing voltage dip on the circuit tripping the UPS.
I would be careful connecting laser printers to consumer UPS products. On paper all the numbers may line up, but I don't know why you'd want to if you could otherwise avoid it.
If the printer causes your UPS to trip when merely sharing the circuit, imagine the impact to the semiconductors and other active elements when connected as a protected load.