Make a SMPS from scratch 100% reliable

Job ID: 32795695

Budget: €8 – €30 EUR

I would like someone to show me how to make myself an already reliable SMPS as small as possible. What I want is to supply a pcb relay board (relay driver) which consumes about 0.5 A.

So a SMPS 230V A.C. to 12V 1.25A in the output would be fine I think.

Please, only people that have experience with SMPS and already constructed someone.
Freelancers PRO or amateurs that will just copy stuff from internet will just waste their time with me.

I would like to have the schematic and links for every component (banggood, ebay).
Of course, for the bobbin and the wires needed, as well. Or better a link to buy some ready
which will fit to the needs of the required flyback transformer.

I work with the EasyEDA.