The most common and most likely answer to this crossword clue is the 7 letter word STAFFED
I've seen this crossword clue in The Daily Telegraph
S
T
A
F
F
E
D
Buddy explains!

The straight part
We know that "Supplied personnel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case supplied personnel = staffed.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STAFFED mean?
STAFFED verb- To supply (a business, volunteer organization, etc.) with employees or staff members.
- Occupied by staff, having members of staff.