Mac – Why does the MagSafe power connector only work one way round

Here's my theory. The magsafe connector, head-on, looks like this: [**.**] What I write as "*" looks like an electrical contact. It really only needs to connect two things (the "+" and "-", possibly ground too). To allow you to plug it in either way, it must be designed symmetrically. So for example it could be wired so that the two external contacts are connected to "-", and the two internal ones to "+".

Now, contacts can get damaged over time. What might have happened is that, say, the magsafe's rightmost contact does not work anymore. So you have something like [**.*.]. By sheer bad luck, it might be that the corresponding contact on the laptop side also does not work anymore.

So when you plug it one way, the leftmost outer contact works and does the job. When you plug it the other way, each side has a broken contact and so the circuit cannot complete.

Here's a pictorial version:

           orientation 1      orientation 2
magsafe    [**.*.]            [.*.**]
computer   [**.*.]            [**.*.]
(result)   works!             does not work

edit: checked the actual wiring, and it is indeed symmetrical as I describe.