I think "Đầy" is "fulfil" or "full" ( water , liquid ) , "đủ" is "enough" .
Example :
- Ly nước này đầy rồi ( This glass is full of water )
- Mọi việc làm tới đây là đủ rồi . ( Untill now everything is enough )
"Đầy đủ" is popularly used , too . Its same to "full" or "completely .
Hope my answer will help somehow .
Thank you for reading