I believe I'm actually going to go for either a 11.1V or 14.4V series of C or D batteries. And the way I'm running it is im having one lead go directly to the ps2's motherboard and having another lead go to an adjustable voltage regulator

that outputs 7.5V for my intec screen.
Though I'm not sure how much diferent the PsONE screen is but im sure you can just use a voltage regulator. Unless the 7808 is cheaper It could be simpler for you to use.
Just another option though.
