The utility model discloses a direct-current power supply device of a transformer substation. The power supply device comprises a preceding-stage power supply, a backward-stage power supply, a systemcontroller and a lithium capacitor module, the pre-stage power supply is used for providing a low-voltage direct-current bus to be output to the post-stage power supply and the system controller and charging the lithium capacitor module; the post-stage power supply is used for receiving the low-voltage direct-current bus and providing a load voltage value for the transformer substation; the systemcontroller is used for monitoring the power supply device and sending monitoring information to the monitoring background; and the lithium capacitor module is used for automatically switching to lithium capacitor discharge to maintain the output of the low-voltage direct-current bus to the post-stage power supply and the system controller in case of failure and power loss. According to the powersupply device, the lithium ion super capacitor module is used as an energy storage medium, the lithium capacitor is automatically switched to discharge to maintain the output of the direct-current buswhen the alternating-current fault loses power, switching is not delayed, bus oscillation cannot be caused, and the power supply device has the advantages of being high in power density, long in service life, free of maintenance and the like.