Here is a quick little guide for low profile EE type SMPS flyback transformer core selection.
The recommendation here is based on some assumptions:
- 5kHz – 200kHz switching frequency
- Double E shape, wire wound transformer
- you have calculated winding turns and and wire thickness correctly
Core Model vs Power
And that should cover your requirements for SMPS design in the range of 1 to 100W!
There are a variety of different cores available in this range and for higher power ratings. Flyback topology based SMPS designs are extremely effective and low cost to around 250 watts of output power.