wall adapter standard

If you're referring to the wall plugs with integral transformers and rectifiers, commonly known as "wall warts", with the round output plug with a hole in the centre - I'm not sure about those sold in America, but here in the UK, there doesn't seem to be any standard. Usually the inner pin recess is positive, and the surrounding sheath is negative, but sometimes it's reversed. Often they print a small diagram on the housing or the plug to show this, but I usually test them with a multimeter just to make sure. Some of the general purpose replacement models have an option to reverse the polarity, along with a voltage selector, presumably because of the lack of standardisation.

Tom