if you inject power from another source, you might run into issues like were discussed when people wanted to use multiple rail power supplies...
why not...
run another cat 5 cable from another port on the same hub out to the other end of the string, then use those 3 pin connectors to attach the power to the opposite end of you lights (with data NOT connected)
so you would have a 3 pin male connector on both sides of the string (the far end wont have data connected)
one cat5 cable running to your ssc with data
one cat5 cable running to the far end with + and - with no data connected
or...
use a 2 pin connector on the far end to avoid confusion