The OID for the power supplies is: .1.3.6.1.4.1.11.2.14.11.5.1.55.1.1.1.2
If you do a snmpwalk on it it returns something like this:
iso.3.6.1.4.1.11.2.14.11.5.1.55.1.1.1.2.1 = INTEGER: 3
iso.3.6.1.4.1.11.2.14.11.5.1.55.1.1.1.2.2 = INTEGER: 3
These are the states of a power supply:
1: NotPresent
2: NotPlugged
3: Powered
4: Failed
5: PermFailure
6: Max
7: AuxFailure
8: NotPowered
9: AuxNotPowered
So what this means in this example is:
Power Supply 1 and 2 are powered.
I hope I could help you