Did you try reseat it ?
it should not go like that if the ps is the same 4200 on each ps unless it maybe be a software related issue or something to do with what its actually connected back into
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/25ew/configuration/guide/conf/pwr_envr.html
Note 
All Catalyst 4500 series switch AC-input power supplies require single-phase source AC. The source AC can be out of phase between multiple power supplies or multiple AC-power plugs on the same power supply because all AC power supply inputs are isolated. Each chassis power supply should have its own dedicated branch circuit: 20A for North America and circuits sized to local and national codes for International locations.
When you insert power supplies in your switch, use power supplies that are of the same wattage. If you mix power supplies, the switch will use the one it recognizes first and ignore the other power supply. The power supply status displays as err-disable and the summary displays as all zeros (0) for wattage values in the output for the show power command.
The following example shows the output for the show power command for mixed power supplies:
Switch# show power
Power Fan Inline
Supply Model No Type Status Sensor Status
------ ---------------- --------- ----------- ------ ------
PS1 PWR-C45-2800AC AC 2800W good good good
PS2 PWR-C45-1000AC AC 1000W err-disable good n.a.
*** Power Supplies of different type have been detected***
Power supplies needed by system :1
Power supplies currently available :1
Power Summary Maximum
(in Watts) Used Available
---------------------- ---- ---------
System Power (12V) 328 1360
Inline Power (-50V) 0 1400
Backplane Power (3.3V) 10 40
---------------------- ----
Total Used 338 (not to exceed Total Maximum Available = 750)
Switch#
