Isle's receiving investment, primarily in electricity supply perhaps (5)
I believe the answer is:
'electricity supply perhaps' is the definition.
'isle's receiving investment primarily' is the wordplay.
'isle's' becomes 'mans' (Man is an example**).
'receiving' is an insertion indicator.
'primarily' indicates taking the first letters.
The initial letter of 'investment' is 'i'.
'mans' enclosing 'i' is 'MAINS'.
'in' acts as a link.
(Other definitions for mains that I've seen before include "current public source" , "seen in cockpit" , "Distribution network" , "Source of electricity or gas" , "They're located in cockpit" .)