In this article, a new methodology for the sizing of a fast-charging station for electric vehicles is presented. The proposed method is applicable to public service vehicles on urban journeys. Its use has been conceived for vehicles equipped with an energy storage system based on supercapacitors (SCs), which are already functional in several countries. The proposed charging station also uses a bank of SCs of variable capacitance. During the study, mathematical expressions will be obtained for the electrical variables involved in vehicle charging: instantaneous current, peak current, charging time, dissipated energy, and the efficiency of energy transference. From these, each of the components of the system will be dimensioned: the capacitance of the charger with its different variable steps, the initial voltage of the charger, and the current smoothing inductor. The proposed charger presents the advantage of allowing energy to be evacuated to the electric vehicle very quickly and with high performance, all without using an external power source or high-power converters. The proposed architecture minimizes the disturbances that, with conventional methods, would appear on the electrical grid, preventing the installation of fast-charging stations at many grid nodes, as is currently the case. Finally, the charger control algorithm is considerably simplified as it only depends on the initial voltage of the vehicle’s accumulator.