12VDC

Most board cameras, mini cameras and about one third of the professional cameras work with 12VDC, 100mA to 200mA for B/W cameras and 150mA to 300mA for color ones. These cameras usually have DC jacks to accept DC power plugs. You should be careful about the polarity (positive and negative) for this power source. 12VDC power can be supplied by AC Adapter or battery pack. You may even use a "power cord" plugged to the cigarette lighter in a car.

24VAC

About two thirds of the professional cameras work with 24VAC, 20VA to 40VA. The cameras usually have screw type connections and you don't need to worry about the polarity. This power is usually supplied by AC Adapter and you need to prepare separate power cable for the connection. Unlike 12VDC, this power can be transmitted to a long distance up to 450ft and is proper for the cameras that are to be installed outdoor or when you don't have the power outlet near the camera.

DIN Cable

When a camera is connected to a monitor by DIN cable like in most "observation system*", the power(usually 12VDC) is supplied from the monitor so that you don't need to worry about the power for the camera.(* The "observation system" means the monitor has a built-in quad splitter or switcher and has usually 4 DIN jacks. But, some observation systems which are packaged by dealers or retailers may have a monitor without DIN jack and the power for the camera should be supplied separately.)