Power to raise money externally (7)

'power' is the definition.
(I've seen this in another clue)

'to raise money externally' is the wordplay.
'raise' says the letters should be written in reverse.
'money' becomes 'pence' (I've seen this before).
'externally' means one lot of letters goes inside another (some letters go on the outside of others).
'to' in reverse letter order is 'ot'.
'ot' inserted within 'pence' is 'POTENCE'.