Supplied by a G-man? (3)
I believe the answer is:
fed
This clue is a double definition.
'supplied' is the first definition.
(feeding is a kind of supplying)
'a g-man?' is the second definition.
(I've seen this in another clue)
'by' is the link.
(Other definitions for fed that I've seen before include "Banking authority" , "Given sustenance" , "supplied with power?" , "Provided courses" , "Dished up food" .)