What is the difference between ferrous sulphate and ferrous ascorbate?

They are different kinds of iron salts. Each kind of iron salt may have a different composition of elemental iron. Dosage must be calculated based on salt form. Ferrous sulfate is 20% elemental iron. Ferrous sulfate, exsiccated, is approximately 32% elemental iron. Ferrous gluconate is approximately 12% elemental iron. Ferrous fumarate is 33% elemental iron, for example. The pharmacist would have had to substituted something that was bioequivelent and they probably would have had to ok the substitution with your Dr. so it is likely that they will have the same effect on the body.