Last time I looked into the MIBs, there was not support for monitoring power supply or fan status.
When you find an OID that might give you your data, you can query the Nexus device to see if the OID is supported.
The first command to run is "show snmp internal oids supported create". This creates a table of what OIDs are supported on that firmware.
Then you can run "show snmp internal oids supported" and looks for the specific OIDs that you're hoping to monitor.