With you having the 4 drive configuration you have the 480watt non redundant power supply. Unfortunately the server can't be made to handle redundant power supplies, it is a different chassis for the redundant power supply version. 
I dropped a new processor and memory in this server over the weekend and realized it only had a single power supply. It looks like it may have an expansion slot for a second but it's really not clear. The server has become too important to have a single point of failure.  I am used to servers having quick release power supply's which pop in and out without ever having to open the lid, that's clearly not the case on this model but I would like to be able to hard wire one in if possible. Thanks.
Redundant Power - Dell R510?