0Phil B 11 years ago For an historical perspective, you ought read on George Westinghouse and Thomas Edison. Edison promoted DC current systems for municipal lighting grids. Westinghouse promoted AC current systems. Westinghouse won. DC does not travel far on transmission lines before voltage losses mount. AC can travel quite some distance without degrading. Modern electronic devices employing semi-conductors need DC current to work, but connect to AC line current. The power supply steps the voltage down to a practical level and rectifies it, that is, converts it to DC.