A power supply device (1) for at least one electrical means (2) arranged below sea level, for instance a power supply and control device, or the like, used in maritime oil and/or gas production, comprises a voltage supply means (3) particularly provided above sea level, which is connected via a first cable connection (4) to the electrical means (2) and via a second cable connection (5) to a subsea anode (6). —The electrical means has assigned thereto a subsea cathode (7) for closing the circuit. It is thereby ensured that power supply is guaranteed even in the case of reduced cabling efforts for a long period of time and can be maintained and repaired in a simple way.