This might also be just a Cisco IOS bug. I've had a similar case with a 3750 where SolarWinds reported the PSU as Not Functioning but the output on the device is OK. Cisco have it listed under bug ID: CSCtx16194 with a fix in IOS 15.0(2)SE3.
The bug mentions only one PSU but in my case I had two with the second PSU marked as Not Functioning instead of Normal.
According to the bug report the following IOS versions are affected:
12.2(1)SE5
12.2(35)SE
12.2(35)SE1
12.2(35)SE2
12.2(35)SE3
12.2(35)SE4
12.2(35)SE5
12.2(37)SE
12.2(37)SE1
12.2(40)SE
12.2(40)SE1
12.2(40)SE2
12.2(44)SE
12.2(44)SE1
12.2(44)SE2
12.2(44)SE3
12.2(44)SE4
12.2(44)SE5
12.2(44)SE6
12.2(46)SE
12.2(46)SE1
12.2(46)SE2
12.2(50)SE
12.2(50)SE1
12.2(50)SE2
12.2(50)SE3
12.2(50)SE4
12.2(50)SE5
12.2(52)SE
12.2(52)SE1
12.2(53)SE
12.2(53)SE1
12.2(53)SE2
12.2(54)SE
12.2(55)SE
12.2(55)SE1
12.2(55)SE2
12.2(55)SE3
12.2(55)SE4
12.2(58)SE
12.2(58)SE1
12.2(58)SE2
"Thank you so much for sharing the information. I researched on this issue for the problem you’re experiencing with power supply status returned incorrectly when you run snmpwalk, your 3750 IOS is hitting the bug id: CSCtx16194. Please visit the link given below for more information:-
http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCtx16194
While your device is running 150-2.SE2, the fix is integrated in 150-2.SE3 and later. I checked few similar cases and the same has been confirmed by the backbone team. IOS 150-2SE3 has an ETA around May 2013.
Unfortunately, there is no workaround for this issue. This happens randomly on some power supplies affected by this bug. You may try to reload the switch that shows incorrect status, but it may be a temporary fix."