I am using a combination of quest, NOW, healthaid and bio-health [british i believe].
If you are in america you have a much wider choice and it’s about half the cost of us brits. In general look out for sugars, this includes maltedextrin and probably anything ending in -ose. The rest is a combination of natural substances, fibres and other natural stuff generally considered inert.
Most of it is either natural stuff your body is taking from other sources or its been shown to pass through you with no effect.
Try i-herb i am in the uk and even i am going to go through the rigarole of having stuff shipped over from them, cheaper and great choice too.