Vitamin C sourced from foods is the most potent/powerful source compared to supplements I've found through personal experience and research. Not only do these foods come with very high Vitamin C content, but also fiber, antioxidants, polyphenols, astringent properties, and many other health promoting benefits!
Highest vitamin C foods - Oranges, chili/bell peppers, broccoli, kale, papaya, strawberries, kiwi, mango and many others! (most fruits have very high Vit C content)