you dont necessarily need a voltage regulated PSU
the tittle may or may not seem a little controversial but ive found it to be true. i dont need an expensive PSU, even if i could get hold of one, or to gracefully handle my PC startup/shutdown. I went for the ultra small, cool running 200W snap-on PSU, great form factor.
I dont worry about all those little problems concerned with comming out of hibernation, could care less if my USB devices remain powered or not and can use my carPC for hours on end with or without my engine running and startup times are measured in just a few seconds. Ive found another way to power my carPC and screen, totally separate from my car battery, theres plenty of it about and its totally free.
a slight proviso up front though, this technique may not be for everyone but it works just fine for me and the problems just melt away.
ive never been a fan of powering anything from a cranking battery, they're designed to give a big kick when you turn the key and thats it. trying to get 240V to my tent one summer led me to deep-cycle batteries. a different animal, designed specifically for steady power drain all the way to empty with no real adverse effects. i use the factory fitted charging electrics in my car - im pretty sure all cars have them - to charge it up using a $15 split charge relay. the charging electrics go all the way from the alternator to the back of the car and would normally connect up to a tow bar if one was fitted, their role is to charge a caravan battery while you're towing it.
i always shudder at the thought of putting a lead-acid battery anywhere near the inside of my car, deep-cycle or otherwise, and would never do it on a permanent basis, but gel batteries are different again. you can put them in upside down if you want and are much more resilient to long periods of discharge.
gels are normally three times the cost but this is where the free bit comes in. gels are used in wheelchairs so i rang up a wheelchair repair place. it turns out that wheelchair owners are particularly paranoid about running out of juice so they regularly replace their batteries leaving this bloke with rack fulls of nearly new batteries he cant get rid of. he gave me a 110 amp hour battery for nothing, not as big as you'd think but anyway ive got a big SUV so boot space isnt an issue. theres a whole range of sizes though, right down to 25 amp hour one which is not much bigger than an ATX PSU.
the next bit is why you dont need a power regulator. the normal procedure is for the charging electrics to only get power once the car battery is fully charged, it gets priority, it means these electrics are fully isolated and switched off during and for a short time after cranking, so, no voltage spike. meanwhile, and even during cranking your carPC has all the power it needs from being connected to your second battery, all it sees is a smooth constant 12V, probably going up a few tenths of a volt more when the charge power eventually comes in.
the upshot of all this is my carPC can be used just as i use my computer at home, just push it to S1 standby when i dont need it or just leave it on, my PSU runs cold so theres no heat build up. ive got a 100 amp alternator that very quickly re-charges any depletion in the gel once i get driving again.
worse case scenario is i dont start my car for three days and forget to power down the PC, the gel does flat, so what, the split charger isolates my car battery so the car starts as normal, it then gets to work charging the gel.
i went back to the wheelchair bloke and took over 1500 amp hours worth of batteries, im going to create one hell of a UPS for my home network, didnt cost me a bean.