A direct current power supply system includes at least one first input source, a second input source, a phase shifting transformer set, a rectifier set and a monitoring module. The phase shifting transformer set is for converting a medium voltage alternating current of the first input source and/or the second input source to a low voltage alternating current. The rectifier set is for rectifying the low voltage AC to a low voltage DC. The phase shifting transformer set and the rectifier set are disposed either in a power supply housing, or in two adjacent power supply housings. The monitoring module includes a phase shifting transformer monitoring unit for retrieving at least one of temperature data, voltage data and current data of the phase shifting transformer set and a rectifier monitoring unit for retrieving at least one of temperature data, voltage data and current data of the rectifier set.