The invention discloses a power supply device suitable for a constant-voltage repeater or splitter of a submarine observation network. The device comprises an input filter circuit, a starting power circuit and a CV-CV series switch main circuit, and a load filter circuit. A DC high voltage is connected to the two ends of the input filter circuit, and the starting power circuit and the CV-CV seriesswitch main circuit are connected to the output end of the input filter circuit in parallel. The input end of the CV-CV series switch main circuit is connected with two ends of the input filter circuit, and the output end is connected with the load filter circuit. A high voltage is transmitted to the starting power circuit after being filtered by the input filter circuit, and the starting power circuit generates a starting voltage to trigger the CV-CV series switch main circuit; the CV-CV series switch main circuit converts the high voltage into a low voltage and transmits the low voltage toa load through the load filter circuit. The device disclosed by the invention supports a wider voltage input range, the conversion efficiency is up to 90%, and the power loss is effectively reduced. The device is simple in structure, high in redundancy, small in size and high in reliability.