Below alarm can be seen on the switch:

root@switch> show chassis alarms
1 alarms currently active
Alarm time Class Description
2023-03-01 17:53:06 UTC Major FPC0: PEM 0 Not Powered


However, the power supply is not lacking power and reports as up from other investigations
root@switch> show chassis environment pem
localre:
--------------------------------------------------------------------------
FPC 0 PEM 0 status:
State Online
Airflow Front to Back
Temp Sensor 0 OK 30 degrees C / 86 degrees F
Temp Sensor 1 OK 37 degrees C / 98 degrees F
Fan 0 5120 RPM
Fan 1 5632 RPM
DC Input: OK
DC Output Voltage(V) Current(A) Power(W) Load(%)
12 7 84 9

PEM status shows OK.

root@switch> show chassis environment no-forwarding
Class Item                          Status    Measurement
Power FPC 0 Power Supply 0          OK        38 degrees C / 100 degrees F
     FPC 0 Power Supply 1          OK        36 degrees C / 96 degrees F

In the logs, we don't see any PEM not powered or PEM failure logs.
The LED light status of the PEM shows GREEN.

This is an indicator of the PSU working fine but the alarm is not cleared. Below steps can be performed to troubleshoot the issue.

1) Restart alarmd process.

>start shell user root

%ps -auwx | grep alarmd

%kill -9 <PID number>

2) Reboot the device with the hypervisor knob

>request system reboot hypervisor at now

3) Re-seat the PEM for which the alarm is seen

4) Test with a known working PSU.