A power module includes an outer shell, a circuit board, plural electronic components and a power transmission interface. The power transmission interface is electrically connected with the plural electronic components and partially exposed outside the outer shell. The outer shell includes a first lateral plate and a second lateral plate. The second lateral plate includes a first protrusion portion and a second protrusion portion. The first protrusion portion and the second protrusion portion are protruded relative to the first lateral plate and respectively located at two opposite edges of the second lateral plate. After fastening elements are respectively penetrated through a first fixing slot of the first protrusion portion and a second fixing slot of the second protrusion portion and tightened into a case of an electronic device, the power module is fixed and installed on an inner surface of the case.