This type of power supplies are readily available in market. You have to specify the rating, that is how many amperes the intended circuit will draw. But if you intend to make one your self, buy a 110 to 15 V step down transformer, 4 diodes, 1000mfd capacitor and an ic "7812". That will provide 12v stabilised 12v, which can handle 1A current.

Buy one cheap model 12V car charger from any car parts store. Take all the parts from it,then put them into your project as you made.

How many amps does it need

Isn't cheap but here's one for 40A: http://www.jameco.com/webapp/wcs/stores/...

I need to convert house power to automotive power to progress on a project I am working on. I searched the net, for what seemed like an eternity, but with no results. If anyone out there could help me out it would be greatly appreciated. Need a device with a regular three prong plug for ac input and screw mounts for the output, like what you would find on a car audio amp. Thanks in advance