# Which end of a barrel connector is positive

I am having trouble understanding barrel connectors. From what I read online either the inside or the outside can be positive or negative depending on the direction of the current.

SO which end is the positive and which is the negative. Any useful advice or articles of this would be great.

This is the kind of connector I am talking about:

Thanks, Dan.

• It is whatever it is hooked up as. There is no standard, the tip (center) might be positive with respect to the ring (outside) or not. – R Drast Apr 29 '15 at 14:37
• The end that measures positive with your multimeter is positive, and the end that measures negative is negative (assuming you have one at an actual wallwart) – PlasmaHH Apr 29 '15 at 14:38
• @RDrast: In my experience the sleeve is the negative more than about 80% of the time. This seems to be some kind of rule, with exceptions (see comments): electronics.stackexchange.com/a/33969/5163 – 0x6d64 Apr 29 '15 at 14:54
• It isn't a rule by any means. I am looking at three power supplies right now. Two the sleeve is positive, and one it is negative. Saying it is a 'Rule with exceptions' means that it isn't a rule. – R Drast Apr 29 '15 at 14:57
• "either the inside or the outside can be positive or negative depending on the direction of the current." This doesn't make sense to me. The positive part is positive and the negative part is negative regardless of which direction the current flows. If current is flowing into the positive part then the device the plug is attached to is receiving power (would be a little against standard use of these kind of plugs). – Austin Apr 29 '15 at 15:25

The + sign is connected to outer shell in this example, meaning that the outside of the connector is positive and the - sign is connected to the black dot in the middle, meaning that the inside connection is negative.