Keeping tradition with doing things backwards, I've finally got a UPS for the rack (mounted in the bottom of the stack). Got a PowerWalker VI 2200R. Its a 2U unit which is all the space I've got left in the rack. Decent price and decent I/O with USB, serial and a slot-in for network expansion + 4 IEC outputs. Its powering everything in the rack and connected via USB to my main server which runs a NUT server that other machines can connect to. A calibration run (100-80%) puts the runtime at about 20 min. Long enough that I'm comfortable setting things to shut down when 20% capacity remains. Summary, I sleep better now.
Depends on how much you spent on your PC, and how reliable your grid power is. Ours is decent, but we get windstorms that create variation in the transmission. 13 years ago I didn't bother with UPS but then we had a power failure, back on, failure , back on, all within a second or so. Killed my Dell Powersupply and graphics card blew one hdmi port. Since then I have had one. had to change the battery last year for $80. It has saved me from brownout when a crow vapourized itself on the transformer outside our place. And every few months the logs show voktage correction for overvolting AC. it is cheap insurance that your syatem is getting clean power. Last month my laptop charger power pack shorted internally, so UPS immediately shutdown power. Even if it wouldn't have overloaded the laptop, it possibly prevented a fire since the short was not enough draw to blow the panel breaker.