does ups limit my psu

[pppotatoes]

hello, this is my first post so please forgive any mistakes i may make
i have seen a post about how ups limits the psu if its W is lower than the psu's W
what i dont understand is, why would an ups limit the power output when there's no blackout. doesnt it only turn on when there's a blackout?
to give an example for clarification, can i use a 100w ups on a computer with a 750W psu that constantly uses 400W until a power outage, or would the pc simply not turn on even when there is no blackout?
(i know almost nothing about these stuff, so im sorry if my post doesnt make sense)

 

[alceryes]

The PC would work fine. The UPS will give whatever the socket its plugged into gives. Watts and voltage can vary depending on location, wiring, breakers, and distance from a sub station. Here in the states most plugs commonly give up to 15A at ~110V which adds up to about 1650W max.
When you draw more than what a UPS battery can supply it usually just starts beeping at you as a warning. It's basically saying that if the current draw persists, and the power goes out, the battery won't help you - it's all going down.
As long as the power stays on everything will run fine though.

 

[InvalidError]

As alceryes said, if your UPS is under-rated for the load you have on it, it may cut off altogether if an outage occurs. Some UPS have limited overload capability and will operate for a few seconds on overload to give you chance to dump load (ex.: allow your PC to switch to a battery power management profile) before cutting off.

 

[ARICH5]

a ups should be used for emergency purposes only. if the power goes out and the ups saves the pc from spiking, save your work and switch it off as normal. its not supposed to be used for continual work. thats a back up generator is for.