Repairing a so-called power brick is usually not recommended, for reasons of electrical safety.
To emphasize this, power bricks are usually glued or welded shut and cannot easily be disassembled. It would be possible to cut open the housing and effect simple repairs (such as replacing a dead capacitor, common cause of power brick trouble) but the repaired power brick will no longer satisfy safety regulations.
The reason for this state of affairs is that it is not at all unlikely for non-experts to compromise the "safety barrier" between the mains voltage and the output side of a typical power brick, and such may have lethal consequences.
Bottom line: power bricks should be replaced, not repaired.