Electronic – How to tell polarity expected of a DC barrel jack


I'm sure this information is somewhere around the internet, but I can't find it.

I have a device that takes a DC barrel jack. I don't know the polarity it expects though. There is a marking though. It looks like this:

---  12VDC

I'm 99% sure it's a symbol to indicate the polarity, but which is it? Positive inside or positive outside?

Best Answer

Unless there is a figure like below, or some wording like "positive centre" then you can't tell.

DC markings


enter image description here

A supply can use positive or negative centre, as Olin says there is no standard. This is why you get the polarity switches on many of the universal DC supplies.