4mm Plug with central pin. It is similar in design to Probook Laptop charger (which is 7 mm) but smaller and used in power supply/charger for some HP Laptops and old Uniden GPS.
If somewhere in Auckland that I can pick up - would be great.
Even if it is old from the dead power supply - I will re-solder.
Here is the photo of the female part the plug should fit into:
