Re: UPSes are a common feature of...
Funnily enough one of my more dramatic (OK, terrifying) UPS failures was also with a big Dell branded APC rackmount UPS... those have some very large capacitors in them which make very loud noises when they are unhappy. When you're the only one in the building (and it's not your building and you can't get to the main power switch without leaning over the exploding UPS) it's even more exciting!
I do have some experience of bigger Riello UPS - not sure on capacity off-hand but they're the big floor standing units on castors (with a train of big batteries on castors too). Had a couple of them fail too (in a non-exciting manner) but to be fair they're working in a pretty warm and not particularly dry environment.
For all that, the most scary for me was the much smaller 1500VA APC I previously had looking after my PC... I noticed a weird acid kind of smell when I came through the door one morning, eventually traced it to the UPS which was too hot to touch for more than a split second. Somehow I managed to rip the cables out and literally threw it out the door before it set fire to anything; the batteries had been boiled to death and were swollen enough to have become one with the case of the UPS.
I haven't a lot of confidence in these devices for some reason!