Upgrade your SM-PCE01 to be compatible with the new 12Spd SD300 Connections with this SM-PCE02 PC link cable. 

This is the cable that plugs into the SM-PCE01 or SM-PCE02. 

The stand SM-PCE01 PC Link cable has an SD50 plug and therefore cannot be used with the SD300 12Spd Di2 components. 

Shimano's new SM-PCE02 PC link cable has an SD300 plug, allowing you to plug it into 12-speed Di2 components.