Totally insulated switched mode power supply

A totally insulated switched mode power supply for producing a supply voltage for an electrical device, comprising:

• an electrically conductive housing part;
• a first electrical conductor and a second electrical conductor, an electrical conductor of the first and second electrical conductors being for connection to a phase conductor and another of the first and second electrical conductors being for connection to a neutral conductor of a grounded AC or three-phase power supply system;
• a first Y capacitor and a second Y capacitor, the first and second Y capacitor providing asymmetrical interference suppression of the switched mode power supply, and one capacitor of the first and second Y capacitors being connected between the first electrical conductor and the housing part and another of the first and second Y capacitors being connected between the second conductor and the electrically conductive housing part;
• a further Y capacitor;
• and
• a device configured to detect which of the first and second electrical conductors is connected to the neutral conductor based on a phase angle of a fault current indicating a leakage current flowing from the electrically conductive housing part to a ground potential, and configured to connect the further Y capacitor between the electrically conductive housing part and a detected conductor of the first and second electrical conductors.