A power plug adapter with a magnetically attachable module is provided. A signal transmission device is connected with the power plug adapter and the magnetically attachable module. At least one magnetic unit is arranged on the power plug adapter, and at least one counterpart magnetic unit is arranged on the magnetically attachable module. When the magnetically attachable module and the power plug adapter are arranged to have attachment surfaces thereof adjacent to and facing each other, the counterpart magnetic unit of the magnetically attachable module magnetically attracts the attachment surface of the power plug adapter to have the magnetically attachable module and the power plug adapter attached to each other magnetically.