The Q&A sheet mentions that with dual 1150W power supplies, an RPS can backup 1 or 2 3750-E switches.  This is assuming the switches also have 1150W power supplies installed.

But what if they’re only using 750W?  The RPS would have a total of 2300W of power, while three of the switches would only require 2250W.    So it should be able to backup three switches, right?

Nope.  You can only backup two.  So, there’s actually really no point of installing 1150W power supplies in the RPS.

Switch#show env rps
DCOut State Connected Priority BackingUp WillBackup Portname SW#
----- ------- --------- -------- --------- ---------- --------------- ---
 1 Active Yes 6 Yes Yes FDO1525Y1T5 1
 2 Active No 6 No No <> -
 3 Active Yes 6 Yes Yes FDO1417R07E 3
 4 Active No 6 No No <> -
 5 Active Yes 6 No No FDO1406R1KU 5
 6 Active No 6 No No <> -

Yet another reason why the RPS sucks and StackPower on the 3750X and 3850 series is so much better.