Sort of plug more suitable after promotion (7)
I believe the answer is:
adapter
'sort of plug' is the definition.
(adapter plug)
'more suitable after promotion' is the wordplay.
'more suitable' becomes 'apter' (more apt).
'after' means one lot of letters go next to another.
'promotion' becomes 'ad' (short for advert).
'apter' after 'ad' is 'ADAPTER'.
(Other definitions for adapter that I've seen before include "sort of plug" , "'Apt, dear!' (anag.); a switching device" , "Dear Pat (anag)" , "Plug device" , "I could modify" .)