Our profession is not one to buy rather than build...
Personally, I would buy a module every time. I have designed my own but tended to have all sorts of issues with EMC. When I costed my last effort, I realised that the module was significantly cheaper than what I had done. Now I only roll my own if there is some reason why a bought in module won't work (operating altitude, required clearances etc)
it sounded like this electronics forum for hobbiests should never existed. leave all of this to professionals, we? do what we do for a living... not electronics. if we need electronics then just buy it with our savings... now i'm not saying you are wrong, i'm saying the argument is perfectly valid, from different part of the world...
so where's the fun? as most people said... granted by building on our own it can cost much2 more than buying mass produced stuffs. but this thing is not about money alone, some say because its custom to our needs, some say we know our stuff and some say, we gained knowledge, and knowledge is power. what i hate is i buy a stuff and when it broke i dont know where to fix, esp expensive stuffs that we trusted should last for years, this is electronics for the dump era, so... ymmv...
I've always found it strange, seems like a completely taboo topic in electrical engineering. Tons of resources for really esoteric stuff like RADAR, SDR, FPGAs etc. but there's a big hole in common knowledge for probably the most common piece of electronics - off line regulators.
you can find some schematics online but details explanation, characteristic report, hands on experience etc detail stuffs is pretty limited, so i guess if we have to go further we are on our own, maybe the better bet is snap a schematic from the net and then use own imagination, read some theories, slam down some components on perfboard and dont die. the most important part is dont die so you can have the chance telling the world. make ready some tin foil cap, current probe, glove googles etc. make sure you got the circuit properly fused so if anything whats the name of the guy.... lemme check jw notes... yeah if mr murphy happens, you got controlled destructive area, wear google everytime you start a mains. that sort of advice. whats mystery in this subject is the magnetic or inductive force in the transformer thats hard to imagine for me at least, so make sure HV current probe is around and start small... there is one mystery guy keeps posting videos here, rbola i think i'm going to follow his post when i'm in the mood of building this stuff i dont know if he's real or bluff... but the most important thing is... dont die.. good luck!