Is it really safe to use UPS rated lower than PSU wattage (as long as it is higher than the max system power draw)

[CheekySparrow]

I know there are tons of topics about this however would just like to double check if anyone had any unexpected experience. My rig uses 850W Thermaltake Toughpower PSU. I'm shopping for CyberPower UPS; CyberPower 1500VA (900w) is not available in my area, only 1300VA (780W) is. 780W is obviously lower than my PSU max wattage, however, I used online calculator and my system should draw 500W max. I guess I can add 25-50W for monitor, and still be safe with 780W UPS, correct? I'm not planning to do SLI or anything.
Any insights are welcome.

 

[clutchc]

You don't need to match your PSU wattage. That wattage rating is simply the max power the PSU can safely supply. If your rig doesn't demand more than 780W, then the UPS will be fine.

 

[Paperdoc]

IF that PSU is the Gold version, its typical efficiency is 90%. So if you system is actually using 550W (including monitor), the PSU is consuming 611W from its source. A 780W UPS certainly can supply that. You have not commented, though, on how long that UPS can supply 611W when the power fails.