Unofficial power supply in emergencies (8,5)
I believe the answer is:
eminence grise
'unofficial power' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'supply in emergencies' is the wordplay.
'supply' is an anagram indicator (in a supple way).
'in'+'emergencies'='inemergencies'
'inemergencies' with letters rearranged gives 'EMINENCE GRISE'.
Can you help me to learn more?
(Other definitions for eminence grise that I've seen before include "One exercising power in the background" , "Power behind the throne" .)