Power supplied by energy source in sudden intake (4)
I believe the answer is:
gasp
'sudden intake' is the definition.
(I've seen this in another clue)
'power supplied by energy source' is the wordplay.
'power' becomes 'p' (symbol in physics).
'supplied by' is a charade indicator (letters next to each other).
'energy source' becomes 'gas' (I've seen this in another clue).
'p' after 'gas' is 'GASP'.
'in' is the link.
(Other definitions for gasp that I've seen before include "Short laboured intake of breath" , "Struggle for breath with open mouth" , "Inhale sharply with astonishment" , "Utter breathlessly" , "Noisily breathe" .)