I sat the leg of my chair directly on my phone charger cord and severed it in two. Now I need to know what polarity the part that plugs into the phone is supposed to be. It's a small, flattened kind of plug, sort of like a mini USB plug. Is there an engineering convention that dictates the outside terminal (the obvious flattened metal can thingy) is always one polarity or the other? I'm afraid if I hook it up incorrectly I could fry something inside the phone.