A power control device for dynamically adjusting frequency includes an electric transformer, a controller, a loading feedback unit, and a switching transistor. The electric transformer includes a first side induction coil connected to an input power unit, a second side induction coil connected to a loading unit to generate an output power by electromagnetic induction with the first side induction coil, and an auxiliary induction coil generating a power sensing signal by electromagnetic induction with the first side induction coil. The loading feedback unit generates a loading feedback signal. The controller determines the level of loading based on the loading feedback signal and further detects the valleys of the power sensing signal so as to change the switching signal which controls the switching transistor at the optimal one of the valleys.