The Big players when I designed and built computer rooms were Emerson, Liebert, Excide, EPS, Tripp-lite. THe APC units I have seen are not what I am looking for, too small, not enough battery Square wave outputs. (I hooked up an Osilliscope to one.... I must be one of the last people on earth that know how to run one)
My ideal UPS is a single phase unit, 12 - 18 KVA, (the type IBM gave away with the first AS400's) and I would love it it use a Feroresonant (sp) transformer. It was a trick used by cheaper UPS that produces a nearly square wave to make a sine wave, and all the associalted harmonics. The transformer smoothed out the sinewave. It was cheaper than a multileg SCR setup to produce a true sinewave. They could also call this an ONLINE unit because the transformer worked like a capacitor and gave the vendor time to turn on the UPS durring a power failure. It should have 1 hour of battery at 100% load. I'm only running 2.5 Kva at night so I should have some good ride through.
If not, most allowed for more batteries to be added. It would also allow for Solar and Wind charging to be applies as well. Also, most UPS have lots of inputs for controls and alarms.
This means that when running on Listor, it charges batteries and provides power, and if the Listor stops, power continues to the house while I sort out the problem.