The rule about what you can use is:
Rule 4--Equipment
* EVERYTHING - Everything you use in the competition area directly or indirectly for strategy (mission-related activity) must be made entirely of LEGO-manufactured elements in original factory condition.
So, if you can find an appropriate adapter that is manufactured by LEGO, then it would be allowed. I don't know if there are any such items. I did a quick check at BrickLink, and didn't see anything right away. I have seen some very long wires, which might serve the same purpose. Be careful, though--sometimes teams have to be creative to keep excess wire from spilling away from the robot and messing things up!
Steve Scherr
VA/DC FLL Referee Advisor