Extract from: http://www.overclock3d.net/reviews/power_supply/corsair_hx650w_650w_atx_psu/5
- Stable voltages across all rails
- Reasonably high efficiency with an average of around 86%
- Great looks and tasty modular cables
- Excellent ripple suppression
- Max output around 720w
- All Japanese caps.
- 7yr warranty!
- Not quite as efficient or stable as the HX750w or HX850w
- Didn't like one of the cross-load tests (but as I've said already 3 times, its not likely to be reproduced in real world)
As to the UPS, Yes should do the job.