Hidden supply, notes and coins reportedly? (5)
I believe the answer is:
cache
'hidden supply' is the definition.
(I've seen this in another clue)
'notes and coins reportedly?' is the wordplay.
'notes and coins' becomes 'cash' (I've seen this before).
'reportedly?' indicates a 'sounds like' (homophone) clue (I've seen 'reportedly' mean this).
'cash' sounds like 'CACHE'.
(Other definitions for cache that I've seen before include "memory" , "Reserve" , "(Place in) hidden store" , "Secret store of valuables" , "Collection of hidden things" .)