What do the pins refer to in a DC power jack (such as this)

 

1 is the ring, 3 is the tip, and 2 is the N/C (normally closed) contact. The + symbol indicates that the tip should carry a positive voltage referred to the ring.

 

So pin 1 is -, 2 is ground, and 3 is +?

 

No, the ring will be circuit ground. The 2 - 3 contact is to establish a circuit in the absence of the power plug. There is no firm rule as to the usage of the contact closure.

In fact, you are free to use the jack in any way that makes sense to you in a circuit. The jack can carry a signal instead of power.

Here is a link to the plug end - yours will be the TS plug - http://en.wikipedia.org/wiki/TRS_connector.

 

Ok thanks-DC inputs are much more different than an AC input.

 

1 is the ring, 3 is the tip, and 2 is the N/C (normally closed) contact. The + symbol indicates that the tip should carry a positive voltage referred to the ring.

No.
It is not a stereo jack. It does not have a ring.
1 is the sleeve.
3 is the tip.
2 is connected to 3 without a plug and 2 disconnects from 3 when there is a plug.

 

What about this type?

 

Similar, except 3 is a male center pin, and 1 contacts the sleeve.