Ac112

Hi everyone I have just purchased an ARC pro sunset speedway Scalextric and need advice on 2 things. one the box it says 2x 15v transformers but in the instruction only states 1. i have just purchased a C4056 mclaren 720s police car and 2 C3711 monster trucks. questions do I need two transformers the police car and trucks only work on one track with one controller if I switch the digital to analog why is this? thank you in advance