An electrical power supply of an X-ray tube. A high voltage generation device having a primary capacitor is configured to transmit a high voltage to the X-ray tube. At least one voltage source is configured to supply the primary capacitor. An energy storage device has an auxiliary capacitor that is configured to receive from the primary capacitor a quantity of energy and to return said energy to the primary capacitor. A control device arranged in series between the high voltage generation device and the storage device is configured to connect or isolate the storage device from the high voltage generation device so the X-ray tube is powered by a variable high voltage very rapidly between a first high voltage and a second high voltage.