@Codeschubse It's the pictogram for a center-negative barrel power connector. Most electronics have center-positive connectors these days, it's considered a standard by many. (A bunch of music/guitar devices being the notable exception.) So whenever you run into a center-negative device but don't have the original power supply around, chances that you don't find a matching power supply are low, while chances that you destroy the device by accidentally using the wrong one are high. Spooky!