RE; The pin he's talking about would be the adaptor's
While I'm not 100% certain as I do not know the device you are asking about when they say Pin = Positive it means the pin in the middle of the Power Socket of the device not the plug. These Sockets are generally speaking a round hole with a pin up it's middle.
So in this case the Outer metal casing of the actual Male part of the Plug is Negative and the hole down the middle of the Plug is Positive.
I personally do not like those Universal Adapters as I've seen way too many instances where they get pulled out and plugged in incorrectly. OK if there is a Bridge Rectifier in there between the Power Socket and the rest but this doesn't happen much. If you have to use this Adapter make sure that it can not be pulled apart as when this happens the device has a 50% chance of being destroyed when it's plugged back in.
If I have not explained that well enough for you post back and I'll try again if someone else doesn't beat me to it. 
Col
edited for clarity I hope. :0
For 12vdc adaptor, does pin = tip = centre ?
Working for small, small organization which just moved. The wall wart for our Gnet Modem/router BBOO73 went missing in the move. Part no longer available. Gnet gave me the specs so I could find a universal one.
All specs understood, and adaptor purchased from R.Shack., BUT the barrel can be installed as tip- or tip+. R.S. instructions say rotate tip according to what the little polarity diagram is on the device. Could've followed that OK, but no such marking on the device. (pffft to Gnet for that one) Gnet tech guy said "pin positive" in his email. Cool. So what's it mean? Hence . . .
naive Q#1: He was talking about the adaptor when he said pin+. The pin he's talking about would be the adaptor's "send" end, not the little pin in the modem's "receive" end, correct?
naive Q#2: Does pin+ = centre+ = tip+.
crux of the matter: the distal end of the wall wart's cable has a little mark that says "tip". When I stick the tip in, do I want the + or the - to line up with the tip?
I'm sure it's pretty straight forward for you guys, but for newbies, it's like . . . OK---on the receive end there's the lining of the hole plus a pin. On the adaptor, there's the barrel outside and the barrel inside, but no pin, unless... the whole thing is a pin not to be confused with the pin at the receiving end . . . [scratching head]. I think I know the answer, but I need confirmation so I don't fry something.
Thanks.
Kirk
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