What can i expect when switching from simlac to enfamil?

Nothing special: If you are changing from the cow milk based product of one for the other, there is no significant difference in the products that could cause a predictable problem. If you change from a cow milk based to a soy there will likely be some change in stool frequency or consistency.

Depends on baby: Although some babies don't mind which formula they're on, some do better on one than the others. Time will tell -- if your baby doesn't tolerate Enfamil (i.e., diarrhea, constipation, spitting up more, etc.) but did well on Similac, then switch back to Similac.