Google is your friend! The above links should give you some really good insight into SMPS, PWM, and power supplies in general. I would have written up an explanation, but Wiki has done such a good job, I figured I'd let the pro's start you out! You can also Google for images of the same topics you asked about and see a great variety of power supplies, parts, circuit boards, etc.
Thanks for your interest and I hope you gain some valuable insight you can use ; )