Transistor based SMPS supply designing

I always heard about the designing of a power supply based on parisitic components (R,L,C). Lots of designer have been designing the supply on the basis of various topology. But what if I design a power supply based on transistor combinations. Let's know that I need only 3.3V/50mA current at the output from the AC source. So there are lots of combination in transistor in order to get this requirement. If I use a combinations of common emitter configuration, Voltage divider biasing or feedback biasing with the current mirror configuration then is it posible to get these requirements?

I also spend some times on internet but I didn't get relevent answer to solve my query. If this thing is possible then what are the pros and cons of these designing with the normal (using topology) designing?

Well for that you need to put current limiting circuit which can be designed by two transistors. And for that specific voltage output you first need to make two voltage dividers that will be making the transistors to switch for less then 235V so that your circuits remains safe when there is a power surge. and the other transistor to provide you with the specific voltage. May be i am missing something but its almost like this way! Sorry if my info is wrong!