I am unsure as to what's happening, but my cat eats well high quality dry food but often throws up when eating even a teaspoon sized bit of wet can food. I do not understand this. Anyone has any clues?
My Imhotep does the EXACT same thing and has an incredibly sensitive stomach. I just stopped trying to give him wet food as he obviously can't handle it, but I have a kitty water fountain and he drinks a lot of water from there.
If the cat is healty, feed him what he likes, rather than trying to give him stuff his stomach can't handle. Just watch the ingredient list on your dry food - it can change from batch to batch to some degree and the same applies to tinned food. Watch the water intake.