When I had a UPS that could handle 2 servers.
Not just one, but bunches of them. This was before we could afford the total data center battery. So every system I put in included lots of UPSs.

And each server had 2 power supplies.
And each power supply had it's own UPS.
That could handle 2 systems, but was dedicated to that box.

My uptime was phenomenal, including riding through lengthy blackouts.