hot power supply

The power supply for my iBook G4 gets pretty hot.
Jd Lyall wrote on :

The power supply for my iBook G4 gets pretty hot. Once it got very hot and stopped charging. I unplugged it and put it on the cold window sill. After it cooled off it worked again.

Do these fail often? I guess I should get a backup unit if that is the case. From some other supplier. Who makes the most reliable power supply for these things?