>UPS's are rather magic bullets (and pretty good monitors) of strange things.

The vast majority of times, yes. However, I've had two instances of failed UPSs causing freaky problems (had a hard time convincing the users to buy new ones [out of warranty] based on those experiences :-))

I also had another case where a fully functional UPS caused major problems. At a remote site several notebook PCs, portable printers, and 10BASE-T hubs were powered off a gasoline generator. Really shitty power - perfect application for a UPS, right? Wrong - this is what happened:

- Under the applied load, and with the long power leads from the generator, available voltage was only just over 100 volts. This was below the "brown out" threshhold of the UPS, so it would kick in to boost the voltage up to 118 or so. It did this by cutting off the generator feed and supplying power from its batteries.

- With the load removed, generator voltage went back up to just over 120. UPS detected that, went off line, putting the load back on the generator. That looped back to step 1 above and repeated for several hours.

Eventually, the UPS batteries ran out of juice, as they never had a chance to recharge at the low available voltage from the generator under load. When the UPS was attempting to top up the voltage, there was nothing left and the voltage to the load was actually dropping to zero. The batteries in the notebook computers spanned those dropouts, but the hub didn't, causing network disconnects. Eventually noticed that, when the UPS beeped and "switched on", the hub power and connection lights went *off*. Hmmmm.....