I work at a computer repair shop in Marietta, Georgia and we have a lot of spare power supplies laying around. This tutorial will explain how you can take a generic computer PSU(power supply unit) and turn it into a power supply that will power your Arduino and give you all the amperage you need as well as your standard 3.3 volts, 5 volts, and 12 volts for any accessories/electronics used on your breadboard .
Step 1: What you will need
1. A Standard Computer Power Supply Unit.
3. Soldering Iron + Solder
4. Male Headers
5. A plug that fits into the Arduino's DC Jack (I got mine from an old keyboard power cord)
6. Heat Shrink Tubing (optional)
Step 2: Which PSU suits your needs?
On the side of most PSUs there is a sticker detailing the maximum amount of amps for each rail. I chose a random power supply because that did not matter so much to me, but some people might be picky.
Step 3: The Pinout
We will be cutting a Molex or a SATA("L" shape) power connector and splicing the wires
Black - Ground
Yellow - 12 Volts
Red - 5 Volts
Orange - 3.3 Volts
Step 4: Sata vs. Molex
If you only have Molex connectors, you will notice two grounds, a 12 volt, and 5 volt wire. In the case that you only have Molex we will have to cut into the large cable you see here in order to get 3.3 volts.
If you have some SATA connectors on the other hand, those have two grounds and and 12, 5, and 3.3 volt wires. No need to cut into the large cable for 3.3 volts, unless you want extra. Otherwise skip this step
Step 5: Short the Green and Black wires
Your PSU will only turn on if the green and black wires are shorted(as shown above). You can use a small piece of wire or solder to short them or you can cut the two wires and solder them together.
Step 6: Solder On Your Male Headers
In my example I used cut up paper clips because they were all i had at the time, this was not the best idea because they are slightly to large for the breadboard.