A power supply device for a vehicle comprising: an input terminal; a charge-discharge circuit connected to the input terminal; a first output terminal connected to the charge-discharge circuit via a first switch unit and a first cut-off unit; a second output terminal connected to the charge-discharge circuit via a second switch unit and a second cut-off unit; and a controller connected to the input terminal, the first output terminal, and the second output terminal, the controller being configured to control the charge-discharge circuit, the first switch unit, the first cut-off unit, the second switch unit, and the second cut-off unit, wherein the controller is arranged to detect that a voltage of the first output terminal becomes lower than a first load threshold voltage (Vlsh), the first cut-off unit is arranged to change from a connected state to a cut-off state, and after a lapse of a first predetermined period following a time at which the controller is arranged to detect that the voltage of the first output terminal becomes lower than the first load threshold voltage, the second switch unit is arranged to switch from a state of higher-resistance conduction to a state of lower-resistance conduction in which a resistance level is lower than the resistance level in the state of higher-resistance conduction, characterized in that after a lapse of a second predetermined period following a time at which the controller is configured to detect that a voltage of the input terminal becomes lower than an input threshold voltage, and that the voltage of the first output terminal becomes higher than the first load threshold voltage, and that a voltage of a second output terminal becomes higher than the second load threshold voltage, the first switch unit and the second switch unit are arranged to switch from the state of higher-resistance conduction to the state of lower-resistance conduction. an input terminal; a charge-discharge circuit connected to the input terminal; a first output terminal connected to the charge-discharge circuit via a first switch unit and a first cut-off unit; a second output terminal connected to the charge-discharge circuit via a second switch unit and a second cut-off unit; and a controller connected to the input terminal, the first output terminal, and the second output terminal, the controller being configured to control the charge-discharge circuit, the first switch unit, the first cut-off unit, the second switch unit, and the second cut-off unit, wherein the controller is arranged to detect that a voltage of the first output terminal becomes lower than a first load threshold voltage (Vlsh), the first cut-off unit is arranged to change from a connected state to a cut-off state, and after a lapse of a first predetermined period following a time at which the controller is arranged to detect that the voltage of the first output terminal becomes lower than the first load threshold voltage, the second switch unit is arranged to switch from a state of higher-resistance conduction to a state of lower-resistance conduction in which a resistance level is lower than the resistance level in the state of higher-resistance conduction, characterized in that after a lapse of a second predetermined period following a time at which the controller is configured to detect that a voltage of the input terminal becomes lower than an input threshold voltage, and that the voltage of the first output terminal becomes higher than the first load threshold voltage, and that a voltage of a second output terminal becomes higher than the second load threshold voltage, the first switch unit and the second switch unit are arranged to switch from the state of higher-resistance conduction to the state of lower-resistance conduction.