You need a microUSB cable to do this.
They are actually quite commonly used to power small usb devices, similar to the one used to charge a Jawbone headset. The cable that connects your Jawbone headset to the power block is actually a very short grey microUSB cable that with works with the new Apple TV (2nd Gen black). This short grey microUSB cable can power your Apple TV alone (without plugging mains power) so iTunes can restore it should you feel the need to.
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