Adequate and sufficient both relate to having enough, but they are used a little differently.
Adequate usually means enough for a purpose or standard. It often suggests that something is acceptable, even if it is not especially strong, impressive, or generous. If you say, The evidence was adequate for a review, you mean the evidence met the basic need.
Sufficient means fully enough for what is required. It often emphasizes quantity, amount, or degree. If you say, One page is sufficient for the form, you mean one page meets the requirement.
- Use adequate when you want to stress acceptability or a minimum standard.
- Use sufficient when you want to stress that the amount is enough.
A simple contrast is this: The room was adequate for one night suggests it was fine, but not special. The funds were sufficient to finish the project stresses that the amount of money was enough to complete it.
In short, both words can mean enough, but adequate often sounds more about meeting a basic standard, while sufficient more clearly points to meeting the full requirement.