Did you gradually introduce your kitty to the new food or just change it abruptly?

When you change a cats food, you need to do it gradually. Mix the new food in with the old food and gradually decrease the old till there's no more left, just the new stuff.

When he vomits, does it contain WHOLE piece of food?

If so, he's eating too fast. Better to give him smaller portions.

Check the contents also to make sure he's not suffering from an intestinal parasite.

Also check to make sure he hasn't been eating anything foreign, as Slick mentioned, like plants, rubberbands, small objects.

Does he go outside? If so, he may have eaten something from the outside.