Hi Dee Ma,

I think Felix answered with good points.

Additionally I would not recommend trying to make your own Switch Mode supplies - all the theory and circuits are fine but, and it is a big BUT, the figures of efficiency and output ripple, regulation etc depend on the quality of the ferrites and inductors you use. So if you do not have access to quality components, dont attempt building these switchers.

For safety sake ( of you and the connected circuit ) go in for reputed brands with a CE / UL and certification of the like.

And another aspect is the dynamic ripple content when there is a large change in load - more a problem with poor designs.

Raghu