This is not the best way to build a power supply but it is easy to build and design. It is based on the well known theory of a voltage divider. This is a good low cost power supply for beginers.
UPDATE: I am currently working on a new power supply that has much more current. Check my page to see if it came out.
UPDATE 2: I HAVE DESIGNED A NEW SUPPLY, CHECK MY PAGE TO VIEW IT
Step 1: Parts and Tools
2) pairs of plugs (one pair black and one red)
2) thick wires (red and black)
2) bolts (if needed)
1) four foot segment of solid strand wire
1) 681 ohm resistor (google voltage divider if can't get)
1) roll of electrical tape or heat shrinking tubes
1) perf board
1) Project box
1) 5k ohm potentiometer
1) roll of solder
1) 12 volt adapter
needle nose plyers
Hot glue gun with glue
work gloves (highly recomended for soldering)
Step 2: Starting the Basics
First turn on your soldering iron and glue gun, to get warmed up. And find out which is positve and negitve on your adapter. Once you found them start soldering on some single stranded wire about 4 inches long onto the resistor and POT. Once done put the iron away. Follow the diagram below to get your perf board set up. Glue down any loose wires down along with the perf board to the project box.
Step 3: Finishing Up
Now its time to put the plugs in. Drill 3 holes if needed on outside of box. Insert the plugs with a hole in them. Bolt or glue them in. Also do the same for the POT. After they have been secured solder the corect leads to the plugs. Look at the picture below for what it looks like. Also finish all steps here. Don't forget to solder the other plugs.
Step 4: Your Done
Now that your power supply is finished, You can do other DIY projects. And you don't have to buy batteries! Look at the picture below and ask as many questions as you want. Enjoy, and look for more projects by me.