12 volt power supply:

click here to enlarge the schematic

parts:

U1	LM7812 +12 VDC Voltage Regulator
BR1	4 amp bridge rectifier
T1	18 volt, 2 amp ac transformer
F1	2 amp slow-blow fuse
S1	SPST toggle switch
R1	330 ohm resistor
C1	3,000 uF electrolytic capacitor, 35 volt min.
C2	100 uF electrolytic capacitor, 35 volt min.
LED1	Light Emitting Diode
MISC.	fuse holder, heat sink for U1, binding posts, ac cord with plug, chassis

all resistors are 5 or 10 percent tolerance, 1/4-watt
all capacitors are 10 percent tolerance

Please operate caution when building this power supply. It is run on standard 117 ac current - and under the right circumstances 117 ac can kill you. Use a plastic enclosure if possible to decrease chances of short-circuiting. Don't use the power supply if it's wet, and never run it without the specified fuse.