New food?

Genie threw up this morning shortly after eating a mixture of about 3/4 of old food which they didn't seem to like that well and 1/4 of new food (RC Persian formula, which I thought would be good for their hair and hairballs). Could this have caused her to vomit? Or is it more likely a hairball issue? (She has thrown up once before with a hairball, but this time no hairball was there, only food.) Or something else?

WHat is the old food???

I always tell folks to go very slow with cat s.. 14 days is not uncoomon for a food switch

They were eating Nutro Max Cat. One seemed to like it ok, but the other one didn't. I have also tried the Nutro regular, which they didn't really eat a lot of. The best they ate was when they were eating Iams kitten. But they aren't kittens anymore...
I also thought I would try the Natural Balance if the RC doesn't work out.

The only thing is the RC has corn which Nutro doesnt... I would switch really slow.. You do realize that ave protion on a no corn no by product food is about 33% less??? Okay so that only happend at my house with the dog ... Iams kitten is chn flavored...
I like Natural Balence and if flavor is an issue it may be worth it after a month or so on RC ..Another one to look at is Pro Plans natural.. Which flavors of max and natural choice did you give??

Also, sometimes (just like people) certain foods don't agree with certain cats. Since they liked Iams so much maybe you could switch to Iams adult?