I have various MBPs and a MBA 11", all of which operate using their included official Apple power supplies, which will fit each other as they have the same Magsafe connector but are of different voltages and currents. They seem to work whichever one is used for whichever machine, though I have noticed that some seem to run very hot when used on machines they were not designed for. For example, the main body of the PSU of a MBP 13", when used on my MBA 11" is almost too hot to touch after a full charge. Am I causing any damage to the PSUs / various machines / their batteries by using the wrong power supply or is the technology intelligent enough to deal with this by stepping up/down automatically? I have only briefly tried them to see if they actually work and don't want to damage anything! Thanks for any help!