Voltage Doubler Adapter – 18V or 24V For pedals with higher voltage requirements, the Voltage Doubler Adapter 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 jack for use with any standard power cable with a 2.1mm plug. Ideal for MXR Flanger and Dime Distortion, Crybaby 535Q, and various Fulltone and Keeley products. Power Supply Connector:2.1mm Straight Barrel Plug (2)Pedal Connector:Jack for 2.1mm PlugPolarity:Standard (Center Negative)Length:4 in / 10 cm