A power/data electrical coupler, designed to send over a two-wire bus or to receive therefrom data signals and to deliver to said two-wire bus or receive therefrom a power-supply potential. Such a coupler includes a transformer, a first winding of which and a second and third winding of which are connected in series with each other with a common terminal connected to a power supply line and the other two terminals to a two-wire bus. It also includes a second isolation transformer connected between said first transformer and said two-wire bus. According to the invention, said terminal common to said second and third windings is connected to said power supply line by means of a band-rejection filter rejecting one or more of the frequency bands including the resonant frequency or frequencies resulting from the association of the isolation transformer and the transformer.