Shock from back of generator during power cut (7)
I believe the answer is:
outrage
'shock' is the definition.
(synonyms)
'back of generator during power cut' is the wordplay.
'back of' suggests the final letters.
'during' is an insertion indicator.
'power cut' becomes 'outage' (an outage is a loss of power).
The final letter of 'generator' is 'r'.
'r' put within 'outage' is 'OUTRAGE'.
'from' acts as a link.
(Other definitions for outrage that I've seen before include "Atrocious act" , "Shock horror!" , "Gross violation of decency" , "Extreme indignation" , "Fury" .)