I am using a Morex 3688 case which comes with a 12VDC@5A power brick and an internal PS. I replaced the internal PS with an M1-ATX. I used the original power brick to get things working on my desk before installing in the car. I replaced the two-pin coaxial DC power plug on the case with a 5-pin plug on a flying lead. In addition to the 12V and ground the other pins are for the ignition on signal input, 12V regulated out for my xenarc, and 5V regulated out for future use. I put a mating harness in the car for use there, and I also made one that connects to the power brick. This allows me to bring it inside to run the PC for upgrades or testing. If I were so inclined, I could leave the PC in the car and run it off the power brick via extension cord to the trunk. If I were going to do that regularly, I suppose I would make it so that plugging into the external source would automatically switch over.