As much as I feel Oscar has improved on Wellness, I think your theory gives
the food a little too much credit.  Have you tried different flavors?  Maybe
Mico just can't tolerate something in the Wellness food.

You didn't mention if the food was dry or canned. I know that my cats
sometimes eat dry so fast that they end up puking it right back up. If
the Wellness is wet -- is this a recent development? Has he ever been
able to keep it down? If not, maybe it just doesn't agree with him. You
have two others choices that work, so you should be fine.

eq

Both of my cats have Wellness canned in their diet and have had no problems
with it.  When I used to feed a mix of wet & dry (not at the same time) I
bought a bag of Wellness dry.  They both ate it like candy, but Otto would
throw up every single time.  Sometimes right after he ate, sometimes later
on. As soon as I stopped the Wellness dry, the puking stopped.  Now they get
very little dry food.  If I go away and the catsitter can only come once a
day they get Science Diet dry left out, and once in awhile I'll give them a
little as a treat.

--
Liz

If your cat agreed with the Wellness food I'd expect he would keep it down.

Note this by itself is not an indication that Wellness is bad. It only
means that your cat does not agree with the particular type of Wellness
food you have been feeding it.

Stop feeding him the particular kind of Wellness you have been. It isn't
doing him much good anyway if he cannot keep it down. Start hunting
around for another kind of food, even within the Wellness brand, that
will agree with him if you want to feed three different kinds of food.

They do this sometimes, often because the food is something they
really like and they eat it too fast, or it is "too rich" for them, as
my vet says. You might try putting down just a bit, then waiting
and putting down more, if you are around and have the time.

As others have suggested, perhaps there is something in Wellness that just
doesn't agree with your cat's system.  Some cats just have sensitivities to
certain ingredients.  I would stop feeding it since you say it's been going
on for a while.