Described is an explosion endangered region usable, switching power supply for supplying an output voltage controlled to a desired value, comprising a supply path, which includes a switching controller controlled via a driver, a galvanically isolated transformer connected after the switching controller, and, connected after the transformer, a rectifier-containing, output circuit, and a feedback path, via which the driver is fed a signal transmitted via a light source and a light receiver and reflecting the output voltage, based on which the driver controls the output voltage to the desired value via a corresponding operation of the switching controller. The feedback path includes a voltage regulator, which regulates a supply voltage falling across the light source to a fixed value, and an electrical current regulator, which regulates an electrical current flowing through the light source to an electrical current value corresponding to the output voltage.