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:

enter image description here

Thanks, Dan.

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    \$\begingroup\$ 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. \$\endgroup\$ – R Drast Apr 29 '15 at 14:37
  • \$\begingroup\$ 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) \$\endgroup\$ – PlasmaHH Apr 29 '15 at 14:38
  • \$\begingroup\$ @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 \$\endgroup\$ – 0x6d64 Apr 29 '15 at 14:54
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    \$\begingroup\$ 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. \$\endgroup\$ – R Drast Apr 29 '15 at 14:57
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    \$\begingroup\$ "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). \$\endgroup\$ – Austin Apr 29 '15 at 15:25

The answer may be a bit unusual, but it's neither!

Barrel connector doesn't have a defined polarity. Instead, what you'll have is the polarity set by the device that you want to use, if the device is using DC in the first place. Near the receptacle for the barrel connector, you might see a sign with something like this:

Barrel connector input

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.

In any case, you need to research this for your particular device. There is no general rule.

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    \$\begingroup\$ Usually, negative/ground is outside. Probably because it is safer. \$\endgroup\$ – neverMind9 Oct 31 '18 at 14:35
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    \$\begingroup\$ While this answer is, in general true. It is far from true in the case of laptops and comparable devices (Arduino's, Raspberry Pis etc) where the pin (centre) is positive. How do I know this? Or what evidence is there for it? (a fair question given the market is large and diversity of equipment large). Two pieces of evidence. 1) Universal laptop supplies are easy to buy and I have some. They provide a variety of DC barrel connectors (different sizes) and always deliver pin positive (cannot be reversed) in my experience. 2) It's 2020 and de facto standardisation has progressed significanty IMO. \$\endgroup\$ – Bernd Wechner May 28 '20 at 0:37

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