Ameren Missouri electric customers will see a slight increase on a portion of their bills starting later this month. The Public Service Commission has approved a requested adjustment to the Fuel and Purchased Power Adjustment Charge. The request reflects changes to the costs paid by the company during the period from February to May. It will result in a 40-cents per month increase for the average residential customer. The change will be applied to what is currently a refund of $1.76, resulting in a slightly lower refund of $1.36 per month. The adjusted rate will take effect September 24th.