Quite a simple power supply unit can be built for half an hour.
The scheme is designed for voltage and current of 6.8 V 300mA. The voltage can be changed by replacing the Zener D4 and, if necessary, D3. A setting on the radiators of transistors can be increased and the load current.
Diode bridge – any, is nice and a reverse voltage of at least 400 volts. By the way, we can recall the ancient and diode D226B, once terribly popular.
Scheme is not galvanically isolated from the AC, so when its assembly, setup and use, you must be extremely cautious.
Parts list : R1 : 4K7 R2 : 5K6 R3 : 3K9 C1 : 1000uF/10V D1 : KU405B D2 : KC650A D3 : D817B D4 : KC168 T1 : KT940A T2, T3 : KT815