9V to Barrel Jack Adapter - PRT-09518 - SparkFun Electronics
Amazon.com: Chanzon 9v Battery Clip with 2.1x5.5mm Female DC Connector I-Type Plastic Holder and UL Wire Pack of 5pcs kit for Arduino,LED Strip : Electronics
10pcs Experimental 9v Battery Snap Power Cable To Dc 9v Clip Male Line Battery Adapter For Arduino Uno R3 Diy Jack Connector New - Integrated Circuits - AliExpress
10X 2.1 x 5.5mm Male DC Power Plug to 9V Battery Clip Adapter Cable – Envistia Mall