The most common and most likely answer to this crossword clue is the 5 letter word INPUT
I've seen this crossword clue in The Times
I
N
P
U
T
More clues leading to the result INPUT
- Contribution from trendy place?
- Contribution is not properly used thus at first
- Contribution from one head assuming power
- One fanatic accepting penny contribution
- Enter island by rickety punt
- Contribution is not picked up then, originally
- Initial data turning up in one set of books
- One fanatic seizing power supply
- One new place for contributions?
- Entry of Russian leader, cycling
Buddy explains!

The straight part
We know that "supply" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case supply = input.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 INPUT mean?
INPUT noun- The act or process of putting in; infusion.
- That which is put in, as in an amount.
- Contribution of work or information, as an opinion or advice.
- Something fed into a process with the intention of it shaping or affecting the output of that process.
- To put in; put on.
- To enter data.
- To accept data that is entered.