A present invention provides a PDA with a built-in current limiting device. When powered by a battery, the PDA outputs a current to an external device, wherein the current is within a first current range. When powered by external power through an adapter, the PDA outputs the current to the external device, wherein the current is within a second current range. The first current range is smaller than the second current range. Additionally, a current limiting device built into a PDA is disclosed.