As a PCB designer, I have come up with a 24v , 12v and 0v power supply system for my household use. The power supply is capable of converting 240 VAC to 24 VAC using the 237-1983-ND transformer then rectify the 24 VAC to 24 VDC, then the 24 VDC is regulated using the LM317BD2TR4G. To get the 12VDC we use the L7812  IC . The 0v is obtained from the ground.
 Components;
R1: 15 ohms 5W
R2: 150Ω
R3: 470Ω
R4: 270Ω
R5: 15K
R6: 2.2K 2W
C1: 6800uF 50V [Electrolytic ]
C3: 220uF 35V [Electrolytic ]
C2,C4: 0.01uF 100V Ceramic
BD1: 6A 100V Bridge diode
D1: 1N4007 Diode
LED1: Red LED
Q1: TIP3055, 15A 60V NPN transistor
Q2: TIP32, 4A, 40V PNP transistor
VR1: 10K Pot potentiometer
T1: 230V AC primary to 24V,3A secondary transformer