{wiki}

Positive center is way more popular: https://gearspace.com/board/electronic-music-instruments-and-electronic-music-production/1222518-center-negative-vs-center-positive-power-supply.html

\Image[https://upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Polarity_marking_center_positive.svg/425px-Polarity_marking_center_positive.svg.png]

\Image[https://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/Polarity_marking_center_negative.svg/425px-Polarity_marking_center_negative.svg.png]


 Polarity symbols