You will basically shorten run time.
Your system should not exceed 250w, so it will be fine and not be an issue when it comes to using it (vs the ups rejecting to work cause of "overload" detected), but you might not get more than a few min of runtime before it will run out of juice.
Dont recommend to run it on battery anyway (beyond saving/closing software and shutting down), as all simulated sine wave ups tend to kill psus a lot faster.
If you can, go for the 850VA cyberpower real-sine-wave ups (they have white lcds vs blue backlight).
Check around and even look at the bigger ones of same type, as they sometimes are cheaper when on sale.
The 850 will give you around 10-20min runtime, and about 2min under full load (500w), so even...