Internal + External PSU's?

Just curious to find out. Bare with me.

I'm on a mission to build the smallest gaming PC that I can. (custom case) now, the question is, is there a PSU out there (if possible) that has for example a 300W mini ITX PSU internally plus a cable power supply (like laptops) that supply extra power externally?

It may sound retarded, but its worth a shot if its ever been made. I also asked because I picked up a old PC today (Pentium 4 Packard Bell) and it came with a PSU that had a 2 power inputs. One was a normal 3 pin kettle cable, and the other was a laptop type input (hole connector.) weird right?

Any ideas?