How do cheap power-supplies work? Answered
I was briefly entertaining the idea of making my own power supplies for some electronics projects. Everything I see involves the basic two step process of: 1) Use a transformer between the 110V mains to bring the voltage down to the level you want, 2) Use circuitry to smooth out the current from AC to filtered DC.
However, when I went to price transformers, I quickly discovered that to buy a power transformer rated to hook into 110V AC, the transformer alone would always cost significantly more than the cost of buying a full ready-made power supply of similar output.
You can't buy a transformer rated for 110V for under $20-30, but you can find thousands of cheap wall-warts (transformer plus AD/DC conversion circuitry, plus connectors) for <<<$10. Or, if you look at higher wattage units, you find similarly rated (for volts and amps) power transformers cost $30-100+ dollars more than full power supplies.
How are these cheap power supplies made for the prices they are sold at? What am I missing here?