For pedals with higher voltage requirements, the Voltage Doubler cable will combine two 9V or 12V Pedal Power outputs to create a single 18V or 24V output. This adapter features two BLACK 2.1mm barrel plugs to a single BLACK 2.1mm barrel plug for use with any standard center-negative pedal. Ideal for MXR Flanger and Dime Distortion, Crybaby 535Q, and various Fulltone and Keeley products.