Do you need SMPS circuits?? then let me tell you that the transfomer part is the most critical one. Powersupply designing requires good experience ,if you are new to it you may opt for ready made solutions .If still you want to design a bullet proof powersupply as a first timer, then buy a COSEL powersupply disassemble it and then reassemble it .I gaurantee your powersupply section will never fail in most adverse conditions :) .