A system for supplying electrical power to a plurality of vehicles from a central power supply through a plurality of electrical outlets includes an outlet control unit for each of the outlets and a vehicle control unit for each of the vehicles. The outlet microprocessor switches the supply of power to the outlet to communicate data to the vehicle. The vehicle microprocessor communicates data by switching a load across the power supply to provide interaction between the microprocessors to manage requirement and availability of power. The data includes whether the power plant of the vehicle is gasoline powered, diesel powered, hybrid or electric battery powered. The microprocessor of the vehicle control unit is arranged to control switches which supply power to selected loads in the vehicle and includes an interface which is arranged to connect to a Canbus communication system of the vehicle.