Why does my USB cable have an extra red plug?

My girlfriend just got a new ebook reader — a jetbook — that came with an unusual USB cable. One end is a regular USB mini B head, but the other end has two plugs. Both are USB non-mini A size, but one is red. The manual gives no indication about what the red head does; is it a standard cable type? What is it for? It looks like this:

EDIT: @Chris, Thanks for the answer. It brings up a follow-up question, though: can/should both heads be plugged in at the same time? Or would that confuse or damage the device?

Solution 1:

The black connection provides power and data. The red one is power only. The second cord should be used if the black one doesn't provide enough power to power and/or charge the device. You'll see a lot of external hard drives come with the same type of plug (though usually both are black).

EDIT: To answer your second question, plug the device in using the black cable. If it runs normally and charges (assuming this has a battery), then you're fine. If, however, the device doesn't operate correctly or doesn't charge, then you will need to plug the red cord into another USB port. You wouldn't cause any harm to the device by plugging in both cables. Honestly, the red one would even be plugged into a different computer since it's just power only.

Solution 2:

To answer your follow-up question... The red one most likely only has the charge wires connected, it does not have the data wires connected. If you think about it, it makes sense. The power level is increased but the data transmission comes only from a single source, the black wire. It would not be possible to link up the wires the way they are in this picture and provide a two port data source. You would have collision of signals on the way back (where the wires merge and a single one goes back to the mini-USB). So yea, you can definitely have both plugged in to a single computer. The device would not even probably know if the red one is plugged into a computer or if it's plugged into any other USB device that provides current.

Solution 3:

A USB port can only provide up to 500 mA. The device that cable came with requires more than that, so it must be connected to two USB ports at the same time to get enough power.

Solution 4:

In most cases you won't need both cables plugged in, it's just that there are some laptops (primarily older) that have very low power outputs on the USB ports which require the ability to draw a little more current. From my experience with these devices they won't get confused, but if they work with the primary (black) cable, there isn't much of a need for the red cable. If you just have the red cable plugged in then the drive may spin up, but nothing adverse should happen.

Solution 5:

I have an external hard drive with this kind of cable. If I don't plug in the red cable, I only get USB 1.1. USB 2.0 will not work unless I plug in the red half and provide the extra power.