I have a Westell 7500 without a power supply. I am trying to make replacement. I know that the output voltage is 12VDC 1 amp. I am trying to find out the polarity at the barrel connector (the plug that goes into the 7500 from the power supply). I would appreciate it if some one would look at the little diagram on the power supply and let me know which is positive and which is negative, the center tip or the outside cylinder. Thanks.