This is probably a very simple question but.. I've been trying to find replacement AC->DC adapters for various electronics around the house, but I ran into one which doesn't list its polarity. It simply has "12V 𝌂" printed next to the power socket, without either of the polarity symbols! I found the owner's manual online and checked it, and it wasn't any more specific..
.. So, what does it mean when a device doesn't list its polarity? Is there a default assumption of positive or negative? Or does it mean that the polarity of the power doesn't matter??
Best Answer
If you have a device that is not marked, you can't necessarily assume one polarity or the other. I have, for example, electronic music keyboards and MIDI controllers which sometimes are swapped (Casio is center negative on one, Korg and Yamaha are center positive).
If you have the original adapter, check what its polarity is, either by its label or use a voltmeter to determine its polarity.
If you don't have the original adapter, you could try assuming that the device is center positive, but you risk causing damage to it if it does not have polarity protection. Instead, consult its manual, look online, or as a last resort, take it apart!
If you have an adapter that isn't marked, determining polarity is simple with a voltmeter. If you get a positive voltage then the side connected to the black/common terminal of the meter is negative/ground.