In addition to your situation. You can combine and interconnect two rack-mounted ups to support devices within those two racks. [ check my previous answer ]

Cheers,
taufik kurniawan

there are two approaches for your situation, if I undersatand it corretly.
You want to make two UPS redundant one to another, right ?

First approach, configure them paralely
Second approach, configure them paralel and interconnect the two as standby

Both approaches will have two sources to go to your data centre. And usually go to your rack as left side source and right side source.

the different is that the first approaches you can drive twice amount of power as the second approach to your data centre.

Please note that the devices ( servers, switches, routers, storages, etc) should have two ( redundant ) input power for those both approaches.

Hope that help.