Power or oil frequently turned up in list of investments (9)
I believe the answer is:
portfolio
'list of investments' is the definition.
(as in an investment portfolio)
'power or oil frequently turned up' is the wordplay.
'power' becomes 'p'.
'frequently' becomes 'oft' (synonyms).
'turned up' shows that the letters should be reversed in order.
'oil'+'oft'='oiloft'
'oiloft' backwards is 'tfolio'.
'p'+'or'+'tfolio'='PORTFOLIO'
'in' is the link.
(Other definitions for portfolio that I've seen before include "Case for loose paper, drawings etc" , "Set of papers" , "governmental responsibility" , "Minister's responsibility" , "Large case" .)