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 cable features two BLACK 2.1mm barrel plugs to a single BLACK 2.1mm plug for use with standard center-negative polarity pedals. Ideal for MXR Flanger and Dime Distortion, Crybaby 535Q, various Fulltone and Keeley products. Power Supply Connector: 2.1mm Straight Barrel Plug (2) Pedal Connector: 2.1mm Straight Barrel Plug Polarity: Standard (Center Negative) Length: 18 in / 46 cm