mostly found on SON Dynamos- but occasional found on some Shimano models (J2 Type hubs).
Connector Cap:
 Found on newer Shimano, Shutter Precision, SuperNova and Sturmey Archer hub dynamos.
SL Connector:
 these are only made by SON and are effectively a connection free system- as rather than having caps or spades plug into a terminal on the hub- the hubs axle contacts a connection plate integrated into the fork dropout. These are fairly rare, and only custom frame builders use the SON SL system for the highest level of integration.
In my experience I have found that while most connector caps of the Shimano/ Shutter precision type are interchangeable- I have discovered that Sturmey Archer dynamos connector caps seem to only be interchangeable with ones made by Shutter Precision.