cheap food

i have 3 cats and i usaly feed them high quality cats food however, once in a while when i forget to pick up a bag a the store while shopping, i'll buy the cheep stuff from the corner store. this was the case yesterday night.

on of my cats loved the stuff ihe ate everything i put infront of him faster than he has ever eaten. this moring i gave him his normal food and he would not eat it he just looked at me a howled, so i put some of the crap food down and agian he was in bilss, . i am not sure what to do i know eventuly he will eat the regular stuff if it is there but i feel bad, cause he wants the other stuff he went so far as to get into the cuborad and eat through the bar i found him in thier after he knocked over the bag and spilt it all over the floor,

how bad would it be for him to mix the two as a new food source for him, is there and realy bad , side effects to changinf his diet like that and feeding him some lower qulity food as long as he get some of the good stuff?

One of my cats does the same thing, I use Wellness food but i buy cheaper stuff to feed to the strays in my neighborhood and my cat will knock over the box to eat it, maybe because its a change but she will always eat the good stuff I put in her bowl.