It depends on how you connect it. There is one RPS with three connectors and one EPS with one connector. The RPS has the capacity of supplying redundant power to one switch in a group. In addition, if a switch is oversubscribed in terms of PoE load, the EPS can provide an additional 370 watts of PoE to devices connected to the switch.
In your scenario, if PoE is not oversubscribed on either switch, connect one 1638 to the EPS output and the other to any of the RPS outputs and see if you get the desired results.
If it is connected to multiple switches, the RPS outputs will protect against a failure of the internal power supply or AC input of any one of the switches, but those are shared outputs of one power supply that doesn't have the capacity to supply power to multiple switches.