<August 6, 2010> This power supply configuration should only be used if you can find a positive tip power supply. Negative tip is more common in the music scene (effects pedals). General Guitar Gadgets sells a negative tipped power supply for $11. Check out this post for more info…Adding a power supply to a Cigar Box Amp (REVISED)
It must be noted that not any old power supply will work! Wall warts must be regulated at 9 to 12 volts and no more. A wall wart that is labeled 12 volts, 500mA can deliver up to 20 volts. Only after the current is close to 500mA will it be close to 12 volts. Please be cautious when using an unknown power supply. If you have access to a multimeter, please test your power supply before plugging it into your amp. The LM386 chips will fry in about 5 seconds of over-voltage.