What is the purpose of pin 1 in these power connectors? I have only seen two connectors in the corresponding plug. What does pin 1 do? Is it for a shield?

 

There seem to be no real definitive answer here.

https://electronics.stackexchange.com/questions/10731/wiring-a-dc-socket-why-three-pins
Just speculation.

 

Pin 1 is the center pin of the plug, pin 2 is the outer sleeve. Pin 3 gets disconnected when the plug is inserted.

 

Pin1 1 is the plug center pin and pin 2 make contact to the plug sleeve (pin 3 is open).
Pins 2 and 3 make contact when there is no plug.
This is used when you want to go from an internal source (2 and 3) to an external source (1 and 2).

 

If it's an Headphone socket pin 1, is the ground terminal for the headphones /speaker, pins 2,3 disconnects the internal speaker on plug in of the jack plug.

 

It's the center pin that get connected or disconnected from pin 3 depending on if there is a plug inserted or not. So pin 1 is the sleeve, or 'ground',
Pin 2 is the tip, and
Pin 3 is feedthrough.

 

Pin 1 is the center pin of the plug, pin 2 is the outer sleeve. Pin 3 gets disconnected when the plug is inserted.

I guess I should have looked at the pattern first before posting. That is making sense now thanks.

 

It covers a range of power connectors, the common ones seen on PCCT's are called a Barrel connector, see symbol here.
https://www.digikey.ca/product-detail/en/cui-inc/PJ1-022-SMT-TR/CP1-022PJTR-ND/659915
Max.