NO.
A UPS takes in an AC source from the wall then converts that into a 12V DC source (battery). When you draw from the battery the 12V is converted back to AC again.
There should be no 12V connections to this device externally.
If you want VOLTAGE REGULATION for an AC device you should be using this instead (canadian link):
https://www.amazon.ca/APC-LE1200-1200VA-Voltage-Regulator/dp/B00009RA60
OTHER:
Based on the question, I recommend you do not mess around with electronics in a way the manual does not describe. Bad things can happen.
For one thing a "12V charger" is meant to trickle current to a battery over a long time to charge it up. Voltage regulation involves CAPACITORS to store electrons in case there is a temporary...