be very careful matching polarities with your power adapters. it is possible to completely burn out your unit even if the voltage and amperage are spot on if you mix up the polarity. if you decide to use a universal power adapter read the instructions very carefully.

as far as reading the device, the half-circle or "Open C" in the middle will open toward the polarity that is represented. so if it reads

+ C -

the polarity is negative.

- C +

the polarity is positive.