Hi Laura
The rps2300 is not designed to be a second power in case of a power outage.
It is designed to be a redundance to a power unit failure, that makes the switch that has the failure to still be working, and You can change the power unit on a planned service window.
If You want to have redundance for power outage, You need to have either a switch with 2 psu built in, or 1 rps2300 per switch (or maybe 2 switches).
/Mikael