A power supply system for a railway vehicle is provided including a converter able to receive information from a transmission system between a power supply unit and air-conditioning units and to deduce from this information the demand for electrical power from each air-conditioning unit, this demand indicating the electrical power required by that air-conditioning unit to cool and/or dehumidify the air within a car in which it is installed, and the first electrical converter being equipped with a module for adjusting the amplitude and/or frequency of the three-phase voltage in a power supply network in response to the demands transmitted by each air-conditioning unit.