Booster Flex is a special Flex cable with a little step-up converter built in the middle of the cable which doubles the voltage. You should only use it with low current pedals which draw below 50mA, typically What and drives. You can get 18V from a single 9V outlet or 24V of an outlet set to 12V.
Use the type 1 Booster Flex with the black BOSS standard 5,5/2,1mm center-negative DC-plug with a 9V outlet for the 18V Dunlop Wah, some MXR pedals, Fulltone OCD, or others with a low current draw.
We suggest you only use Booster Flex if you are short of outlets and don’t have two to make 18V or 24V using Stack Flex or Series adapter Flex.
BE CAREFUL when using Booster Flex. There is a risk of damaging one of your 9V pedals by powering it with too high a voltage. Check the specifications of the pedal and if you still have some questions, you’re welcome to send an e-mail to firstname.lastname@example.org.