Generally the RPS has two power supplies and this is enough to support two switches but it will depend upon the total draw. Remember that the RPS has to support the switch AND the POE units. Table 1 is quite clear about what it supports.
The RPS has 6 connections so to get your stack covered, you will need 2 RPS units minimum (4 switches on 1 unit and 5 on the other). That will support a minimum of 2 failures on each RPS but I suspect no more than 3. You might get lucky and be able to supply 3 if you have dual 1150W power supplies both available. Perhaps try it out but if you lose the power to 1 RPS PS then you will be down to 1 switch supported.
I don't know how many power circuits are available to you but if you only have two, and the RPS is also connected to these, you would probably need 3 RPS units so you don't have to try to support 5 switches (of which 3 might be lost). But if you have more than 2 power circuits available and you can spread the load evenly and ensure your switches and RPS units are connected separately, you will get away with 2 RPS units.
Hope this makes some sense for you
