I have a Cyberpower 700VA rackmount one (OR700LCDRM1U), and it's no longer sufficient for how I want it to work. Previously it was sufficient, just powering my cable modem and wifi router, to keep internet alive for 2+ hours on laptops & devices when the power goes out.
Now that I have cameras, and a rackmount PC for BI, I have the PC and POE switch on the UPS too. If I unplug the UPS to simulate a power outage, it shows it'll run 20mins tops, and makes a buzzing noise louder than my wife's vibrator. I don't know if it's the load, or if the PC power supply doesn't like the simulated sinewave, but the PC stays running.
Go with a 1500VA (at least).