Electrical device runs: fierce with it, possibly (9)
I believe the answer is:
rectifier
'electrical device' is the definition.
(I know that rectifier is a type of electrical device)
'runs fierce with it possibly' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'with' means one lot of letters go next to another.
'possibly' indicates anagramming the letters.
'fierce' put after 'it' is 'itfierce'.
'itfierce' is an anagram of 'ectifier'.
'r'+'ectifier'='RECTIFIER'
(Other definitions for rectifier that I've seen before include "Device such as a diode" , "I provide a remedy" , "which allows smooth flow" , "Device for changing AC to DC current" , "Electrical device converting AC to DC" .)