I am using a 9V AC converter for a digitech product. But I notice that there is a pin in a socket kind of thing in the adapter. What is the use of this pin?


I am using a 9V AC converter for a digitech product. But I notice that there is a pin in a socket kind of thing in the adapter. What is the use of this pin?


That looks like the center pin of a standard DC Power Jack (also known as a barrel jack).
Edit: Note that this is just the name of the type of connector, so if your adapter is an AC to AC adapter, it still supplies AC.
The inside of the jack makes contact with the outer contact on the plug, while the pin makes contact with the inside of the plug.
DC Jack:

DC Plug:

They are available in different sizes and diameters. There are lots of related questions you might find useful: