Ten in revised rate not included in original charge (5)
I believe the answer is:
extra
'not included in original charge' is the definition.
I can't tell whether this definition defines the answer.
'ten in revised rate' is the wordplay.
'ten' becomes 'X' (Roman numeral).
'in' indicates putting letters inside.
'revised' indicates an anagram.
'rate' is an anagram of 'etra'.
'x' going into 'etra' is 'EXTRA'.
Can you help me to learn more?
(Other definitions for extra that I've seen before include "An additional thing" , "one added to the score" , "One playing a minor part" , "Actor in non-speaking role" , "person in shot?" .)