Two types of UPSs: Think carefully about which one you want.
One type normally just sits there idle, passing mains current through directly to the equipment. When the mains stops, the UPS starts up and supplies current from the battery system. So the fan runs more or less only when producing power from the batteries.These ones generally produce 'not-so clean' and 'squarer-wave' power which is normally just as useful as sine-wave power. These are generally cheaper systems.
The other type is always on, running continuously, with its fan always on. The advantage of this type is that the equipment always receives its current via the UPS, no matter how much the supply voltage goes up or down. So very useful if you get 'brownouts'.
The UPS gets its power supplied either directly from the mains or from its battery subsystem. These units generally produce 'cleaner' sine-wave power. These units tend to be bulkier and heavier than the pass-through units.
I bought a CyberPower OLS1000E. This machine continuously produces sine-wave current and supplies all the computer stuff on my desk, as well as the WIFI/router and VOIP phone. I didn't have the router and VOIP phone included initially, but I discovered I was cut off from the Internet when just our apartment was without power although the rest of the building and external infrastructure remained powered.
The only drawback I have found in the 18 months or so I have used it is the constant fan noise. When I bought my CyberPower UPS, I probably 'over-engineered' my requirements (I calculated a need for about 250 watts, but the UPS indicates about 50-odd watts in everyday use). Consequently it indicated that it could power my system for up to 24 hours when I actually had an outage. (Though I take that '24 hours' with a grain of salt.)