look for a LCD with a power brick on display at the stores. Read the ratings on the brick. Look for input of 120/240 (house current) depending on where you live and an output of 12 volts with a wire going into the the back of the LCD.
I use a 14" that is powered this way in the car. I trimmed the output cable from the brick and connected it to the 12 volt rail of the PS.