I'm having difficulty selecting the correct UPS for my home configuration.

I have 2 machines I'd like to keep online. We have been having daily power failures (2-4 seconds) and I think that can't be good for the H/W.

So I got a cheap Ultra UPS but it turns out this was completely the wrong choice for 2 systems that have 500 W PSU's each. I'm not sure what I expected, but I didn't expect the UPS to just shut off.

The nominal load for my systems should be around 130 W, and if the GPU is working hard then it could get as high as 400W.

Still I know the rules - I should have gotten at least a 1200W UPS.

So, now is this 250W UPS utterly useless?

4 Answers 4


Many UPS systems will shut down if overloaded as a self-protection and safety measure. Operating the UPS power converter above its rated output could cause it to overheat, potentially damaging the unit or even starting a fire.

Is the 250W UPS useless? No. You can power up to 250W of equipment off of it (How about your cable box and internet connectivity devices (cable modem, DSL modem, router/firewall/switch etc.)

Do you need to shell out the cash for an appropriately-sized UPS for your computers? Yes (at least if you want protection for them).

  • Although 250W is too small for a gaming rig as described, there are some smaller computers that will do just fine. For instance my Mac mini and LCD display together draws <200W at full load (and <100W when idle)
    – David C.
    Aug 11, 2017 at 3:03

You've almost answered your own question, but here's what I would add:

Use the "wrong size" UPS that you bought to power your monitor, switch, and router if it will support that load. Having your computer powered via UPS doesn't do a whole lot of good if you don't have a working monitor. Using it to power your switch and router would be an added benefit so that you can connect to the power company's web site to find their phone number to report the problem.

I can't tell you how many times I've face-palmed wishing I had documented the cable company's phone number from their web site so I could report when my cable internet connection goes down. ;)

  • 2
    You can also use a small UPS to power your DVR, VCR (if you still have one) or fish tank aerator. It's not useless just less useful. ;-)
    – Chris Nava
    Jan 21, 2011 at 21:23
  • Hmm... I do have a VCR... and a record player
    – joeqwerty
    Jan 22, 2011 at 2:26

It's not unusual for UPSes to shut themselves down if they detect an overload condition. Startup-load can exceed run-load by quite a bit, so that by itself can be a problem for UPS sizing. Chances are that 250W UPS is still good, it just need to have less hungry equipment plugged into it. Like the living-room HTPC.


A UPS will warn you when you get close to the limit of their capability. Some will also work slightly over their limit, but if you greatly exceed their capabilities, they will shut off.

Is it utterly useless, for what you bought it for yes. It may be useful for smaller load applications (home router, wireless, etc).

  • "Cheap" UPS systems often don't warn - they just screech once (if you're lucky) and shut down when overloaded. "Good" UPS systems will provide load indications, and it's almost always worth investing in one that does...
    – voretaq7
    Jan 21, 2011 at 20:53

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