I have heard of people using PC Hardware (PSU) to power their car audio systems, and I was wondering HOW? What Wattage would they use? What Brands? How would the wiring work? Etc...
What you've probably heard of is people using PC PSUs as 12v power supplies to power car audio equipment in a house, not while actually in a car. Is this what you're asking about? I don't think I'd ever actually recommend it though, I guess it depends on what you actually want to power.
The only other thing I've seen is people installing PC's into cars and using specialized automotive pc power supplies to drive them.