Sunny82 wrote Where did you buy your extension cable from? Could you post the link? I purchased an extension cable from Amazon with 2.1mm x 5.5mm but it didn’t fit as the barrel was too long. After...

Just bought and wired an extension cable with barrel plug size 5.5x2.1 mm, fits fine. (5.5x2.5 mm did not fit). Router: Deco M9 Plus (Hardware v. 1.1), barrel plug size 5.5x2.1 mm.