The power supply interface (10) includes a rectification stage (18), having an autotransformer (40) connected to a power supply network (12), and a signal conditioning stage (20) having an output (28) supplying power to a load (14). The conditioning stage (20) includes a power module (22), for conditioning the power supply signal, and a control module (24) designed to control the power module (22). An autotransformer (40) includes at least one additional winding (62A, 62B, 62C; 64A, 64B, 64C) connected to the control module (24) to supply it with electrical power, the or each additional winding being magnetically coupled to at least one primary winding (44A, 44B, 44C) of the autotransformer (40). The power is supplied to a motor in an airplane.