user 18 said:
Actually, it depends on the drive. The external drive that I have only needs one of the two prongs to be plugged in to work - depending on how much power the drive draws. Also, at least one drive (that I know of) uses one prong for power and one for data.
Thing is, that port is most likely a USB 2.0 port. USB 2.0 can supply more power through a single port than a USB 1.0/1.1 port can. I have a Maxtor external HD, and its cord has two USB plugs: one for power, and another for data. In my laptop and desktop which have USB 2.0 ports, plugging in just one USB header is enough to make the drive work. In an older machine in a relative's house, I need to plug in both.
That leads me to believe that if the DVD burner was released in a time when USB 1.0/1.1 was still common, then it would be bundled with a USB "Y" cable to get enough power to work. If you plug it to a USB 2.0 port, then it might not need both to be plugged in to work. With the advent of USB 3.0, the maximum allowable current was almost doubled from USB 2.0 (900mA compared to 500mA of USB 2.0).