Unsolved Mystery

A riddle I remembered randomly: how does Superman get his powers back in Superman 2? His mom was very clear on the point that the transformation is irreversible. At least, I would expect there to be an arduous trial of worthiness or sacrifice before he wins back what he threw away so lightly.

It's inexcusable, if you think about it, how the writers of Superman (Mario Puzo? et al?) neglected the perfect invitation to write about one of the most interesting things in the human experience: redemption. In fact it's a creative-writing felony. The only theme in literature that's possibly as interesting as redemption is betrayal, but even that's not nearly as powerful, I think, and it requires a lot more skillful buildup in order to be delivered effectively.