The present invention discloses a power adapter has a power converter, a power output cable, a first DC power connector and multiple second DC power connectors. The power converter has a casing, a power converting circuit mounted in the casing, and an AC power inlet and DC power outlet electronically connected to the power converting circuit. The power output cable has a DC output and selective connector having two DC power pinholes and multiple selective pinholes surrounding the two DC power pinholes. The first DC power connector has two DC voltage pins and is selectively connected to the DC output and selective connector. Each of the second DC power connectors has a body, a DC plug formed on the body, two DC voltage pins formed on the body and one jumper pin formed on the body and corresponding to the selective pinholes of the power output cable to change voltage of the DC power output from the power converting circuit.