An add-on adapter 110 enables a single charging port 102 of an electric vehicle charging station 100 to simultaneously charge two electric vehicles. An adapter controller 120 determines the available charging rate offered by the charging station. Electric vehicle charging handles 150A, 150B are determined to be connected to the electric vehicles. A charge sharing control circuit 300 in the adapter controller, determines modified available charging rates to be offered for simultaneously charging the electric vehicles. The modified available charging rates are based on the connection states of the electric vehicles and the available charging rate offered by the charging station. The adapter controller controls two contactors 130A, 130B to switchably connect a charging station power socket to the electric vehicle charging handles, to provide shared power at the determined modified available charging rate to the electric vehicles, for simultaneous charging.