This is named the HP Barrel Adaptor. It’s a 4.5×3.0x0.6mm Male 5.5×2.5mm Female connector for connecting most standard 5.5mm output cables, such as that provided with the Voltaic V88, V250, and V72 battery packs, to select HP laptops.
HP Barrel Adaptor Specifications
Positive center pin.
Outer Dimension: 4.5mm
Inner Dimension: 3.0mm
Center Pin Dimension: 0.6mm
HP: HP Stream 11/13 HP Pavilion Series HP Spectre Series HP Envy Series
May also fit other laptops & electronics – check your specs!