Three elements should pay attention before getting start
Voltage, Current, and Polarity
Voltage (V)
You need to know what’s the voltage that the pedal requires (9V? 12V? 18V? or 24V?)
Current
Current is measured in Amps (A), most of guitar pedals draw 100mA (milliamps)
Make sure the power supply has enough current
Polarity
Make sure the positive and negative connections is correct
9V Battery
-Portable power source
-Need to worry about the battery life
-Carbon battery good for analog pedals such as Wah, Fuzz, Distortion, Overdrive
External Power Supply
-Isolated Power
-Fulfill different power requirements (9V, 12V, 18V)
-Don’t need to worry about the battery Life