Hold back the power, or increase it (9)
I believe the answer is:
reinforce
'increase it' is the definition.
I can't judge whether this definition defines the answer.
'hold back the power' is the wordplay.
'hold back' becomes 'rein' (I've seen this before).
'the power' becomes 'force' (force is a kind of power**).
'rein'+'force'='REINFORCE'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for reinforce that I've seen before include "Give added strength to" , "Buttress" , "Make stronger" , "give added support" , "provide support" .)