Many people are happy to design powers supplies thinking they are very simple. On the surface, they are but in reality there are many little pitfalls. I always remember trying to discuss secondary breakdown characteristics of a particular power transistor with an application engineer from the manufacturer. I was rather disconcerted when I discovered he did not appear to know what secondary breakdown characteristics were. Failure to take them into account will not show up in initial testing but could lead to failure some time in the future use as the semiconductor substrate burns away a little bit every time it is used.
If you have an educational project, then fair enough. Go for it, particularly as modern ICs have made the job much simpler.. But always remember that the power supply is the most critical component of any piece of equipment capable of doing the most damage if it fails. If your reputation and money rely on your project, bite the bullet and purchase a commercial design (there will be one somewhere) which will have been manufactured in quantity and been tested properly.
