The utility model provides a portable DC power supply which is prepared for temporary standby application and a test. The power supply comprises a lightning protection device, an AC distribution unit, a charging module, a step-down unit, a control loop, and a centralized control and insulation monitoring unit. The power supply is suitable for small and medium power plants, a hydropower station and various types of transformer stations in a power system, and is also suitable for users of DC equipment (petrochemical engineering equipment, mining equipment and railway equipment). The power supply can provide DC power for the test, can temporarily replace an original DC power supply, and can serve as a standby DC power supply for instruments and meters in a secondary loop, and relay protection and fault illumination occasions. In order to meet the demands of on-site operation, the power supply can serve as a DC power supply, also can monitor the overvoltage/undervoltage conditions of a bus, can be connected with a local monitoring system through a 485 remote communication interface, and achieves a function of remotely and locally monitoring a portable standby DC power system.