Is it alright to use the iPhone plug with the MacBook transformer(?) / power cord ?
I ask this as the MacBook transformer has a bit of metal where the iPhone transformer doesn't.
I already mix the iPhone one with my Airport Express and my MacBook Pro transformer and I never got a problem.
As I just checked now, the metal piece form the transformer doesn't have an electrical contact with the plug part and the iPhone plug, the Airport Express one and the MacBook Pro are the same.
I think they used a metal part because it's stronger.
All Apple products use these same plug parts and they can even be purchased separately from independent resellers. The metal piece is used to support the plug when it is connected and ensure that it plugs in straight.
The plug parts are interchangeable between power supplies without any problems.