Lolwuuuuuuut. Each card does not take 400w. It's 400w for the fulll system. With a 550w you'd be more than able to run 7770 CF.http://www.newegg.com/Product/Product.aspx?Item=N82E16817182200&Tpk=rosewill%20rg630
^ good cheap psu with more than enough power.
BTW, you can't crossfire four 7770. There's not enough CF bridge connectors. Max is two. And after 2 the scaling of each card decreases dramatically. (+AMD CPU's are bad)