The invention relates to a switched-mode power supply delivering a first (VPOS) and a second (VNEG) voltage which are symmetrical. It comprises a power stage (30) comprising an inductor (L), and switches (A, B, C, D, E) controlled by control signals. It also comprises a control circuit (34), coupled to the power stage (30), that is able to produce error signals (Verr1, Verr2) as a function of the difference between a reference voltage (Vref) and the first (VPOS) and second (VNEG) voltages. The power supply comprises a synchronization circuit (38), coupled to the power stage (30) and to the control circuit (34), for generating the control signals in a manner that applies a control strategy adapted to minimize error signals, maintain a non-zero amount of energy in the inductor (L), and maintain the absolute value of the first (VPOS) and second (VNEG) voltages at substantially equal values.