With FireWire or USB, there's no need for an external power supply.   The computer’s FireWire can supply power to the camera as long as the computer has a six-pin FireWire connector and the total power demand on the bus does not exceed the bus capacity.  The computer’s USB can supply power to the camera as long as the total power demand on the bus does not exceed the bus capacity. 

Some laptops have four-pin FireWire connectors; these do not provide power to the camera from the computer.