DC-DC PSU and a mains power PSU are two ways you can power a carpc. DC-DC is more expensive, you need the DC-DC converter itself, and you must build a computer with a relatively low power consumption. But, you'll end up with a cleaner power supply (not that it matters to the carpc itself IMO as long as you are within tolerances). You also have more options as far as startup and shutdown controllers go.

If you use a power inverter, you can use a standard PSU. This method does not cost as much, but it has a few drawbacks. It will most likely put feedback into the power system which you will hear in your audio. It is also not very efficient - you are going from AC-DC (car alternator to rectifier) back to AC (inverter) and then the PSU goes to DC. But, if you have an older computer that is power hungry - it can be a good compromise. -- Why use an older computer? You really don't need much computer power to run most functions.

If I had the money to do it - I would be using the opus DC-DC PSU as mentioned in.


Most prefer a dc-dc psu with startup/shutdown incorperated such as OPUS and M2-ATX. Cost really isn't something you want to spare on these.
Laptops are for cheaters. Actually they generally take up more space with the docks and are a little more expensive unless you have a spare.