DCC is basically a digital system that sends packets of information (commands) to the locomotive such as go forward, increase speed, stop etc. Regular Dc power units have no capability of sending packets of information to the locomotive. Dc is the analog version of control, increase voltage and the locomotive goes faster, if you reduce the voltage, the train slows down or stops. DCC locomotives have addresses similar to your internet connection and you communicate with them by their address. The DCC rails are basically a null carrier until the DCC control unit assembles a packet and delivers it to the rails. The appropriate locomotive will recognize the address and do whatever you instruct it to do. DC locomotives do not have a packet decoder so they are unable to respond to your commands. This is my experience with DCC. I hope it helps.