Experience insufficient energy? (7)
I believe the answer is:
undergo
'experience' is the definition.
(to undergo something is to experience it)
'insufficient energy?' is the wordplay.
'insufficient' becomes 'under' (I can't justify this - if you can you should give a lot more credence to this answer).
'energy?' becomes 'go' (go can mean energy or enthusiasm).
'under'+'go'='UNDERGO'
Can you help me to learn more?
(Other definitions for undergo that I've seen before include "Guerdon (anag.)" , "experience needed" , "Experience, be subjected to" , "Suffer, experience" , "Withstand" .)