An underground power supply system (1,101), in particular an underground vehicle charging station, comprising: - a casing (10,110), to be arranged underground, comprising an opening at the upper side, - a power socket unit (22,122), wherein the power socket unit is movable between a retracted position, in which the power socket unit is arranged within the casing and an accessible position, in which the power socket unit is accessible for a user to connect a charging cable, and - an actuating element to move the power socket unit between the retracted and accessible position, - a cover (20,120) attached to the casing and rotatable with respect to the casing around an axis along a side of the opening between an opened and a closed position, wherein, in the closed position, the cover covers the opening of the casing at least partly and an inner surface of the cover faces an interior of the casing, and - an airtight compartment (26,126,160) arranged at the inner surface of the cover, which is configured to rotate along with the cover and which has a second opening at a side of the airtight compartment opposite to the inner surface, wherein the power socket unit is at least in the closed position of the cover arranged in the airtight compartment, to prevent the power socket unit from getting into contact with water, and wherein the power socket unit is accessible for the user when the cover is arranged in the opened position, wherein the actuating element is configured to move the cover from the closed position to the opened position to move the power socket unit from the retracted to the accessible position, wherein the actuator element is a spring element, arranged to bias the cover to the opened position, wherein the underground power supply system comprises a locking mechanism configured to lock the cover in the closed position and to unlock the cover to allow the spring element to move the cover in the opened position, and wherein the underground power supply system comprises a control unit (30,130) configured to control the locking mechanism, wherein the system comprises a sensor that is configured to measure a water level in the casing and to communicate this signal to the control unit, and wherein the control unit is configured to prevent the power socket unit to be moved between the retracted position and the accessible position, when the water level sensor in the casing measures a water level in the casing that exceeds a predetermined maximum level. - a casing (10,110), to be arranged underground, comprising an opening at the upper side, - a power socket unit (22,122), wherein the power socket unit is movable between a retracted position, in which the power socket unit is arranged within the casing and an accessible position, in which the power socket unit is accessible for a user to connect a charging cable, and - an actuating element to move the power socket unit between the retracted and accessible position, - a cover (20,120) attached to the casing and rotatable with respect to the casing around an axis along a side of the opening between an opened and a closed position, wherein, in the closed position, the cover covers the opening of the casing at least partly and an inner surface of the cover faces an interior of the casing, and - an airtight compartment (26,126,160) arranged at the inner surface of the cover, which is configured to rotate along with the cover and which has a second opening at a side of the airtight compartment opposite to the inner surface, wherein the power socket unit is at least in the closed position of the cover arranged in the airtight compartment, to prevent the power socket unit from getting into contact with water, and wherein the power socket unit is accessible for the user when the cover is arranged in the opened position, wherein the actuating element is configured to move the cover from the closed position to the opened position to move the power socket unit from the retracted to the accessible position, wherein the actuator element is a spring element, arranged to bias the cover to the opened position, wherein the underground power supply system comprises a locking mechanism configured to lock the cover in the closed position and to unlock the cover to allow the spring element to move the cover in the opened position, and wherein the underground power supply system comprises a control unit (30,130) configured to control the locking mechanism, wherein the system comprises a sensor that is configured to measure a water level in the casing and to communicate this signal to the control unit, and wherein the control unit is configured to prevent the power socket unit to be moved between the retracted position and the accessible position, when the water level sensor in the casing measures a water level in the casing that exceeds a predetermined maximum level.