Amperage is a measurement of power usage, or draw. In other words, you don't "feed" amperage to your application; instead, you need to think of your power source as being able to SUPPLY a specific amperage. For instance, the PTH08080 voltage regulator can provide up to 1 amp of current. Above that, you start making it unhappy.
With that said, if I remember, the 12v line pulls the least amps on the board. You shouldn't have any problems powering the screen with it. If you're using a PSone screen and it just shuts off when you try to turn it on, though, do an LED mod and try again. Doing the LED backlight mod drops the screen's usage down to 350mA, IIRC.