As others have said, buy a bigger ups. You can then take your old one and move some of you other gear to it, which make the new one run your server for longer. Ideally something with auto shutdown software.

This is what I ended up doing. I am on my third ups now, and my oldest one is now protecting my desktop.

Yes, having worked in server rooms before setting up home equipment, I chose to use consumer grade equipment. Less noise, less heat, potentially less power. My first “rack” was a wooden storage rack to hold the then 3 desktop towers. I did get the fun of building each system from scratch to get the specific bang for the buck.