Prego has sugar as the third ingredient. Rao's doesn't list sugar at all, and Campbell's owns both.
Prego Traditional reads tomato puree, diced tomatoes, sugar, then under 1% of salt, canola oil, onions, garlic, spices, basil and citric acid. Rao's Marinara reads whole peeled tomatoes, olive oil, onions, salt, garlic, basil, black pepper and oregano. A half cup of Prego has 9g of sugar, 4g of it added. Rao's has 4g and none added.
Tomato paste and citric acid make a sauce sharp, and a few grams of sugar round that off cheaper than cooking it down longer. Campbell's paid $2.7 billion for the company that makes Rao's in 2024.