The HPE P31730-B21-RFB is a server power supply for systems that use a 1U hot-plug unit. Its 800W output at 12V specifies its power capacity and voltage for checking a match with the server.
The 1U format identifies its size category. Hot-plug design allows installation or replacement in a compatible system without removing a standard fixed internal power supply. Choose it for a server that requires a matching 1U hot-plug power supply.