Your power supply lead has two contacts - the bit on the outside and the inner bit. One of these will be positive and the other negative, just like on a battery. When it comes to pedals there is no standard as to whether the middle bit should be positive or the outer bit. They can differ. Usually your power supply will have a "polarity" switch, or you can somehow switch the cable round. Look at your pedal and there should be a diagram either next to the power socket or printed on the label, that should tell you which way round the power should go.
I'm guessing here that maybe the pedal that is giving you problems needs the power the other way round to your other pedals