I have 2 gaming pcs. How do I choose the right nobreak?

So I need to buy a Nobreak to hook up my 2 gamings pcs. I don't plan on upgrading any internal components, ever. One of them has a 2gb gtx 650ti and a 600w ps, and the other one has a 8gb gtx 1070 ti and a 550w ps. So here are my questions:
1: I thought all I had to do was combine the 2 wattages of my two pcs's power supplies, and then get a UPS with the same or higher capacity. Am I right, or there's more to it than just that?
2: Do I only take in consideration the wattage of the 2 power supplies? Because if the power supplies can handle the pcs workloads, the UPS just needs to handle the power supplies, right?
3: If the pc draws more power than the ps can supply, will the ps then draw more power from the UPS? Or does the ps act as a barrier, and doesn't let the pc draw more power than the ps can supply?
 

neeyik

Posts: 1,876   +2,190
Staff member
Power supply unit (PSU) ratings are peak values, and the majority of computers don't tend to come too near that limit. However, it's a starting value with which to judge what rating the uninterruptible power supply unit (UPS) should have.

At max ratings, PSU draw more power from the wall outlet than their rating is - this is because they're not 100% efficient. So if they're only 80% efficient at max demand from the PC, the PSU will draw 125% of that value. In the case of your two PSUs, it will be 750W and 687.5W respectively. Combined, that's way too much for a single, affordable UPS to handle.

So realistically, you're looking at 'normal' power demands - a GeForce GTX 650 Ti has a max power draw of 110W; the GeForce GTX 1070 Ti is 180W. Depending on what CPUs, RAM, HDDs, etc the PCs have, the typical power draw during gaming on your computers is more likely to be 300 to 400W each.

That's still 600 to 800W combined, and a single UPS would need to have a rating of over 600W/1200VA to cope with that - such devices are serious money. You'd be far better off getting two lower rated UPS and running each PC off its own one - something like a 300W/600VA would be appropriate.

That will run long enough for you to safely shut down your PCs, in the event of a mains power failure.