The nexus series switches return an integer value of 4 when it detects a power failure and integer value of 2 if operational.
The power labels are 470 or 471 if the power supply of the switch is damaged. The label 470 and 471 relates to the power supply unit 1 and 2 respectively.
If a fabric extender detects a power unit failure, it returns an integer of 4 for the labels fex_number_000470 and fex_number_000471. For example if the fabric extender attached has an association number of 111, the label will be 111000470 for power supply unit 1 and 111000471 for power supply unit 2.
snmpwalk -c public 10.23.225.166 -v 2c 1.3.6.1.4.1.9.9.117.1.1.2.1.2 | grep -i "INTEGER: 4"
SNMPv2-SMI::enterprises.9.9.117.1.1.2.1.2.471 = INTEGER: 4
In the above example the power supply unit 2 of the switch 10.23.225.166 is failed.