The Lineo5 and Lineo5 Duo use a 2-pin GX-16 connector on the power supply side, and a 5.5 × 2.1 mm DC plug on the device side.
If you need a longer cable, look for one with a 2-pin GX-16 connector and a 5.5 × 2.1 mm DC plug, and make sure the polarity matches the original cable.
Some older product documentation mentions a GX-12 connector. The correct connector is GX-16.