Power Polarity

Thread Starter


Joined May 29, 2018

Feel terribly stupid asking this.

I understand how to tell the polarity of a power supply and how to test is with a multi-meter.

What I am struggling with is
a) how do you tell the polarity of the device you are plugging it into.a
As an example I have looked at my router which has an adaptor

and the manual says
Power12 V ⎓ 2 A

Not positive or negative.Just that

This is just an example I have the adaptor I just want to understand what I would do should I not know?

b) when I do find out does a positive mains adaptor go into a positive identified device
I am assuming so but then I am a project manager and hate that word

Thanks all for your patience.


Joined Aug 7, 2020
From all the devices I have seen, the centre pin is positive except for guitar effects pedals where it is negative.
Any sensible designer would protect the device from a reversed supply.
On the balance of probabilities, therefore, if you assume the centre pin to be positive, you will only do any damage If you have a non-standard device designed by a stupid designer.


Joined Mar 31, 2012
Center-positive is certainly the most common, but center-negative are out there, though I think they are less common than they were a couple decades ago.

A well-produced item will have some kind of polarity indication on both the power supply and the item itself. The most common designation is similar to the following example:


Sometimes it is molded into the case near the power jack.