Are there any other power supply sensors being reported in the EWS sensors tab?
My guess is one of the PSU is bad and hanging the PMbus so neither can be read by the BMC.
If so all the power supply sensors should report unable to read sensor.
Being remote makes it more difficult.
You could remove 1 PSU and see if the FRU can be read on the remaining PSU , if not switch PSU again.
are you familiar with IPMItool or IPMIutil?
Those tools can read the PSU fru data (if the bus is not hung) to see if somehow the FRU has become corrupt.