Gary, the reason you invoke for the use of Wall Warts doesn't seem to exist any longer. Most of the recent electronic equipment come with a multi-voltage transformer, which can then be used with 120/220 A/C (there isn't even an external switch). I believe that presently the only excuse is the final size of the equipment (doesn't apply to a keyboard but can be an important factor in a small preamp or small mixer).

However I have found an advantage using keyboards that need wall warts I sometimes play in churches (weddings) in very small portuguese villages. Either there are no plugs at all or they are very far away for the place where I play (usually in the chorus). So I just use a battery directly:

I have played my Tyros in that type of conditions, but it's a bit more complicated. I plug my battery to a DC-AC converter (12 DC to 220 AC) and then feed the Tyros. Works great and saves me the nighmare of finding a place to plug the keyboard!

-- José.