Power Station NANO is the best power supply system supporting
effect pedals with the finest DC power. Also It is a multi-function
power supply offering 6 normal 9V outputs, one 9V/12V changeable
output, and one 9V/-9V changeable output in a compact size.
-9V is for the effect pedals which use center positive. For example,
Fuzz(with Germanium transistor) and Octavia. And factory setting
is normal polariry(center negative).
Each green LED turns on when output is selected 12V or -9V