Is it okay to alternate between generic baby formula and brand name?

My son is on Gentlease and I seen that Sam's Club carries a generic brand that has exactly the same ingredients and everything. I get WIC and they only give me 9 cans of Gentlease per month and my 6 mo. old son drinks more than that. So I am trying to afford the difference. I only work part time and go to school full-time so I cannot afford alot. Just wondering if it will be fine.