Combine to support energy issue (6)
I believe the answer is:
emerge
'issue' is the definition.
('emerge' can be a synonym of 'issue')
'combine to support energy' is the wordplay.
'combine' becomes 'merge' ('merge' can be a synonym of 'combine').
'to support' means one lot of letters go next to another (in a down clue, some letters hold others up).
'energy' becomes 'e' (physics symbol as in E=mc2).
'merge' put after 'e' is 'EMERGE'.
(Other definitions for emerge that I've seen before include "Come out or become known" , "Develop" , "Materialize" , "Suddenly appear" , "Move out and become visible" .)