Indicates whether a power supply is present:

*Absent* - the device slot is empty;
*PresenceNoOp* - the device slot is uninitialized;
*PresenceUnknown* - the device presence is unknown;
*Present* - the device slot has a device in it;
*Subsumed* - the device slot is configured to be part of another device slot. Not applicable for the fan or power supply bays.