Ok, I found an adaptor for the old PSU EnergYser and the new Xbox 360 S. Got everything hooked up (in the house) and running off an Optima car battery. The Xbox runs fine on the M4-ATX 250W but I am having issues with the auto startup and shutdown features of the M4-ATX. THe M4-ATX is set to P1 (Dip Switch 1 on and 2 through 4 are off). After 5 seconds the M4-ATX's led truns on solid and the Xbox is ready to go but does not turn on. The fan did come on though (because I previously had it on awhile). The Xbox starts up every time manually with the power button. The unit does shutdown on its own but not until after 4 minutes and 10 seconds. On "P1" the M4-ATX is to shoutdown after 1 minute.
Anyone out there working on a similar setup? Do I have to find a way to wire up the (J8) motherboard ON/OFF header (pins 6 & 7)? I hope not as that is what I thought the PSU EnergYser was supose to make this "plug and play". Maybe the newer slim 360 S model and the needed adaptor throws a rench into things?