Might share when supply fails (5,3)
I believe the answer is:
power cut
'supply fails' is the definition.
The definition suggests a singular noun which matches the answer.
'might share' is the wordplay.
'might' becomes 'power' (synonyms).
'share' becomes 'cut' (cut is a kind of share).
'power'+'cut'='POWER CUT'
'when' is the link.
Can you help me to learn more?
(Other definitions for power cut that I've seen before include "turn-off?" , "Go-getter's hairstyle" , "Interruption in electricity supply" , "black out" , "Failure" .)