Abstract: The present invention relates to a power supply unit for a hydraulic system, wherein a sensor is fitted to a spout of a channel of an automatic water supply unit. This sensor is connected to a chip set controlling the opening or closing state of an electromagnetic valve. When objects approach to the spout, the electromagnetic valve is able to be opened for supply water. A power supply unit is disposed at a proper position of the flow channel, and the power supply unit can generate a basic voltage (V) and current (A) by means of the velocity of the flowing fluid in a unit time for creating a basic work (W) for the chip set in opening the electromagnetic valve.