A plug device with a built-in power supply of switch mode power supply type is disclosed. The plug device comprises a printed circuit board upon which a high-frequency transformer, a low-voltage capacitor and other components which make up a switch mode power supply are arranged. A first isolating barrier extends form the housing in between the high-frequency transformer and said low-voltage capacitor. A third isolating barrier extends form the housing and into a first slot in the printed circuit board and a fourth isolating barrier extends from said housing and into a second slot in the printed circuit board. These slots are placed between the high-voltage and low-voltage connection terminals of the high-frequency transformer. A second isolating barrier extends from said housing and between the high-frequency transformer and the printed circuit board and beneath said high-frequency transformer.