For every keyboard I've owned, I do not connect it directly to the mains, but connect it via UPS
- Saves me from fluctuations to some extent
- Gives me a backup for 10 or so minutes in case the power is out, and I can save my work.
I can't give you a specific YES, as I believe the voltage is different in different countries.
Please check the voltage in your area vs what's required (Whether its 230v or 110v) for your instrument and check if your UPS is also giving you the same output and safely go ahead.
It would be a pain to switch on the UPS and then switch on your PSR, but trust me it would save you in the long run from a possible failure, in the long run (especially if you are out of warranty)
Last part
If you are looking to share the same UPS with your desktop AND your instrument, I would not advice you to do that.
UPS have a smaller capacity battery (power source) that can sustain a minimal load at a minimum time.
Overloading it would degrade its performance over time and probably even cause it to cut off suddenly without enough warnings (beeps)
Either, get a separate UPS for your instrument, OR get a higher capacity (bigger) UPS.