What's the difference between the CA 400X cartridge and the CA 400A cartridge?

Technically, CF400A is standard yield toner and CF400X is high yield. The cartridges are physically the same but X has more toner inside. However we are currently selling A and X at same prices because our cost for A is not much less than X. So we only carry X at the moment. If you order A, you will still get high yield X. Please rest assure that all printer that takes A will also take high yield X.