Re: Simple in-car PSU design?

I guess you'll have seen this M1-ATX, but it might be worth a close look
even if you have.

http://tinyurl.com/ymfkt9

There's even one on eBay now too: Listing 170039597684.
Lots of M2-ATX's too, one in UK (160040656843), lots in US. Looks like
less than $80 or £50 will get you one of those. Cheaper to buy US even if
you're in UK, probably, even after paying postage.

Jumpers to set power handling, you can probably set it always on with a
combination of that, and ground pin 4, or whatever pin it is to dupe it
into being on all the time.
.