A power adapter having a replaceable plug has a body having a recess formed in the body and an engagement mechanism inside the recess. A plug, slidably mounted inside the recess, has a bottom board having an engagement mechanism thereon and is slid so that the engagement mechanism of the plug engages or disengages the engagement mechanism inside the recess. A fixing cover is mounted inside the recess and is slidably moved to a first location and a second location. When located at the first location, the fixing cover is located inside the recess, the bottom board abuts the plug fixed inside the recess, and the plug is retrained restrained from moving. When located at the second location, the fixing cover is partially moved away from the recess and maintains a distance to the bottom board, and the plug can be removed from the recess.