A power adapter including a main circuit board and an auxiliary circuit board is provided. The main circuit board has a first surface and a second surface opposite to each other, and the first surface of the main circuit board is configured with a transformer and a first capacitor. The auxiliary circuit board has a first surface and a second surface opposite to each other, and the first surface of the auxiliary circuit board is configured with an input rectifier filter circuit, where the auxiliary circuit board is disposed in parallel above the main circuit board, and the input rectifier filter circuit of the auxiliary circuit board is electrically connected to the first capacitor of the main circuit board. Under a condition of same electrical parameters and dimensions, the volume of the power adapter of the invention is only a half of that of the existing power adapter, which satisfies a demand for miniaturization of the electronic devices.