Has anyone tried fiber powder?

I am taking iron supplements because my hemoglobin levels are low, but I have developed constipation. Even though I am making sure to eat plenty of vegetables and fruits, it hasn't improved, so I looked into it and found out about fiber powder. I read reviews saying it is good for constipation and also effective for weight loss.

I'm tempted to order it because of the weight loss benefits. Has anyone tried fiber powder before?

I am curious to hear your honest review on whether it helped with weight loss or constipation.