I recently got a good deal on a 120V 3000VA APC SURTA3000XL, a 120 pound beast of a double conversion online UPS which boasts over 30 mins of runtime at half load (and that’s still over 1000 Watts)! It didn’t come with batteries, so this video shows the process of “refurbishing” a couple of old modules with new batteries, and testing out the UPS.
The reason I was hunting down reasonably priced DCO UPS wasn’t because I’m especially concerned about poor-quality power from my wall, but because I needed a UPS that would play nice with generator power.
I’d love to be able to afford a couple of ~7500 Watt inverter style generators (one primary and one backup) to run the whole house during a power failure, but the best I can do is a pair of contractor style gensets. They’re noisy and output a mess of voltages and frequencies, but they work. Well, they didn’t work with line interactive UPSes, but they’ll work fine with something like this APC.