It does not matter if it is "wall wart" or battery. Just remember not to exceed 4,5 watts of dissipated power. For example, I had a P8 with 9V output, regulator set to 7V and opticalRendu consuming 1,1A. It mean that regulator board would dissipate (9V - 7V)*1,1A = 2.2W of heat. For M Scaler and 15V regulator "wall wart" or battery voltage should be not more than 19V.