Classic cheme is very familiar but it isn't used in PC power supplies because it has too much weaknesses:

1) It is neccesary to use network transformators, Tr1, which is very expencive and large element and that isn't acceptable for PCs. For power of 200W weight of Tr.1 is aprox: 5 kg

2) Filter capacitor C1 has big numbers of values, in mF wich makes whole thing more expencive

3) Network Tr. has fixed ratio of transofrmation, that means:
Np = Up / Us = 220 V / 5 V = 44
that if network voltage is down from 220 V to 110 V, secundary voltage would fall down from 5 V to 2.5 V. That means that in point Ua from 7.5 V voltage would be 4V. Thats the reason for T1 to stop its work and it would be inverted for a moment. That means this classic PSU (Power Supply Unit) doesn't give very good protection.

4) Transistor T1 is key stability element by which is secured stability of exporting DC (direct current). T1 works in linear amplifying regime which means that his operating temperature is high. Because of high technical disipation transistor requires efficient cooling (Fan + cooler)

5) Classic sheme doesn't give any protection from so called current holdbacks which are present all of the time on network. Classic sheme has protection of overflow and short circuit on output