I have another: do UPS use electricity constantly?

Yes but not much, its a trickle charge to maintain batteries.

Really? Ok, here's the deal anyway:
which PSUs brand+series (APFC, damn it) are most suitable for regular Back-UPS? Like that. Im planning to get 550W PSU, currently looking at SeaSonic SSP-550RT F3

I don't get the question. You make it seem as if the UPS cares what you connect to it, but it doesn't.

Just google "psu with apfc and ups". Most sources say PSU with APFC require UPS to which it's connected have true sine wave -> Smart versions of UPS (not approximate as in Back-UPS).

ps. Im a total noob in this, so I may be just another victim of artificial problems created by marketologists :X

I don't know what's the deal with that... Sounds like FUD to me ;)

All I can say is that I have active PFC in my PSU (not that I wanted it!) and my 8yo Back-UPS CS 500 (that's like the lowest range there is) has no problem with powering this PC and never failed to switch to battery power. And I made it switch a lot.

That's cool, but what is your config and most importantly how is it loaded while switching to batter? For example, I plan to get Season 550W Gold PSU and tests show it successfully switches to battery on 320W consumption and less @ UPS APC Smart 620VA -- and that's a smart version with "clean" sine wave -- with regular back-up UPS you should divide the number by ~1.4-1.5.

PC+2 routers+AP+radio+speakers = 112 W.

The same while running Quake Live = ~200 W. Still switches just fine.

My CRT is disconnected from the UPS as it was possible to overload the UPS (350W maximum or something) when running QW @ 700 FPS :)

CBA running switching tests under different load for you, you're going for a better UPS anyways (I guess mine is square wave?)

I guess mine is square wave?

Yep, afaik all back-ups type is with approximated sine wave.

The same while running Quake Live = ~200 W. Still switches just fine.

Exactly, cause its max capacity is 300W. 200W*1.5 (as I mentioned above) = ~300W :)

For example my cfg: 300W consumption at max (playing some demandable game) + 50W monitor = 350W*1.5 = 525W (while APC Back-ups 1100VA has 660W max).

But yeah, I'd like to hear from experts on UPS of some sort or at least experienced guys :)

Approximated sine wave is like --_--^--_--^--_--

I think mine is square wave: __^^__^^__^^

(Someone bring UTF-8 to ESR finally!)

See, Im not good at terms and at this whole electricity stuff, doesn't really matter to me : D
http://www.apc.com/resource/include/techspec_...tryCode=gb -- Waveform Type: Stepped approximation to a sinewave

Nice, it's better than I thought it was ;) Thanks :)