Ok so I tried hooking up the 12v DC-DC power supply, double checked the original power supply to get the right +'s and -'s, and no worky.
Hooked up original power supply and wired to 120v AC, and it works.
Touched the outputs of the original power supply with the voltmeter, and it definitely is +12v, +12v, GRND, GRND. (The +'s were 11.78v actually)
But giving it 12v and grounds doesn't make it power up, even when using a computer power supply with an 11amp 12v rail.
So my next idea is that the +12v's are not serial but parallel, meaning a total of 24v split in 2, or 2 independent 12v sources.
I'm gonna bridge the 2 outputs of the original power supply and hit it with the voltmeter to checked if it is indeed 24v parallel.
"IF" my theory is correct, then the idea of having a ps2 in a car without using an AC inverter is shot out of the sky like duck hunt.
This DC-DC power supply has some cool features like a auto power on switch lead, for automatically powering on the computer when the remote lead of the power supply is powered.
This would be really useful for automatically booting the ps2 when flipping the power supply switch.
I will post up on here with what I discover, but simply having the 2 +12v's and grounds share the same source is not acceptable.