The present invention provided with a power adapter comprises a housing and a power conversion circuit board mounted in the housing. The housing comprises a body, which is a generally cylindrical shell having an accommodating space, an open end and an opposite closed end, wherein the closed end and the cylindrical shell are formed into a one-pieced, integrated structure, The housing also comprises a side dead wall mounted at and adapted to the open end. The power conversion circuit board has a first end connected to the side dead wall and a second end connected to the closed end, wherein the power conversion circuit board is fixedly accommodated within a confined space enclosed by the side dead wall and the body of the housing.