Answer: Depends on the power of the computer /computers and the UPS
Explanation: For someone who had a big connected network of computers and printers we would plug the computer or server into the UPS as well as the monitor and sometimes a printer sometimes the monitor was plugged into the wall
When you get a UPS you must plug it in for a certain time could be hours or even a day. A USP has a big battery in it and you must charge it (sometimes it comes semi-charged but you must plug it in to strengthen it. )
there are two connector wires that you affix to the battery and you must put a lot of strength into it to make it secure.
So in closing, you can get away with two like a desktop and a laptop.
Read your documentation that comes with the UPS