This depends on what or which sort of external drive itself is a question. As you could categorize this into two, the desktop external drives and the portable external drives. The desktop external drives use electric currents for which you need to plug it into a power outsource. This is while it is connected to the computing device. However, in the case of the portable external hard drives, you can connect it directly to the computing device. These drives don't need to be plugged to an external power source as it works or the power of the computing device itself.