"The power adapter is an optional requirement. In fact, most modern TV's with HDMI 1.4 or higher spec are supported. The Chromecast can draw power from the HDMI port it's plugged into. If your TV doesn't support that, there's also a USB cable and power adapter included in the box. I have a 2012 LG LED and a 2013 Lenovo 27" Monitor with HDMI input and the ports power it with no cable."

Source: http://www.amazon.com/review/RBCJ03NLRAHIF/