Bursar, more confident following adjustment of rate (9)
I believe the answer is:
treasurer
'bursar' is the definition.
(thesaurus)
'more confident following adjustment of rate' is the wordplay.
'more confident' becomes 'surer' ('sure' can be similar in meaning to 'confident').
'following' is a charade indicator (letters next to each other).
'adjustment of' indicates anagramming the letters (I've seen this in other clues).
'rate' is an anagram of 'trea'.
'surer' put after 'trea' is 'TREASURER'.
(Other definitions for treasurer that I've seen before include "Officer in charge of the money" , "Official in charge of finances" , "Financial officer" , "He handles the money for an organisation" , "Financial controller" .)