The LP-E6 is the battery type used in the Canon 60D, 7D, and Canon 5D Mark II. This AC power adapter will power your camera from any AC outlet. There's usually several cameras going at one time and to compliment the stationary tripod shots in the studio, I decided these AC adapters help save me time from charging batteries. I can use my other batteries for the more mobile cameras. Having constant power to a few cameras is also one less thing to worry about when we've got only two guys manning 4-5 cameras. As you can see the cords are very long, so even without an extension cord, they are quite usable on it's own. These cameras don't require much power, and I verified that it works with my little portable $99 dollar battery pack which should give me more than a full day's worth of power. Extended Timelapse shooting? You'll probably think about something like this. If you're in studio, or even on constant location shoots with a static tripod shot, a battery pack and this ACK-E6 battery adapter is definitely a handy thing to have in the bag in case you run low on batteries....
If you're not using a battery grip, you can get away with some of the inexpensive versions running around $20 dollars. If you're using a battery grip, some of the aftermarket types don't work well and the battery door won't close properly. That's why I went with the OEM.
Canon T2i / 550D owners are in luck, as the OEM ACK-E8 power adapter is much cheaper than the ones for the 60D, 7D, and 5D Mark II.
ACK-E8, AC Adapter Kit for EOS Rebel T2i Digital SLR Camera