How to convert old/new computer PSU to get 12V, 15-20Amp rate?
Here is the solution..This conversion must be done by people who have a few years experience in electrical or electronic device only.. Experiment at your own risk.

color code for computer PSU

Wheel of Ohms law formula

No matter how advance our project might be. We must follow this rules.

1.  I personally get this PSU from computer shop. $15 only. rate 250W.(650W above recommended) 

2. There must be a green wire from the bulk. take a black wire(any black will do) solder this 2 wire to toggle switch.This is your power switch. Do not confuse with the shadow. 2 wire only for switch!!

3. Group all yellow wire and crimped them together. by doing this you are concentrate the current all together so you will get high amp without melting the cable. 

3. Group 4 or 5 black wire and crimped them together.(i used two group) for other purpose.

 4. You must connect(solder) brown wire to orange (aplicable for old PSU). New PSU user can skip this step. because there is no brown wire anymore.

 .5. leave all the rest and secure with tape/hot shrink for later use.(make sure they are not short each other.)

6. Optional. You can take any red wire(5v) and connect to LED with black(gnd) make sure you limits the current by using 330ohm resistor.

7. Some psu need preload resistor (10-15ohm 10W) between red and black to cheat them. my psu not from this type. Here is the picture of 15 Ohm resistor.
A new type of PSU have special two additional small wire for sensing purpose. small red and small yellow. You must solder this two small gauge wire to their big brother to make your psu working. 

PS: I remove my switch and permanently solder green wire to black.