Chilli powder can really vary in heat in different areas. A teaspoonful of the chilli powder I get in a bag down the local indian shop is enough for a hot curry for two seasoned curry eaters, and is a lot stronger than cayenne or paprika. The same amount of supermarket one will barely register on the heat scale for me. So when using chilli powder you need to be able to add in stages and perhaps later in the cooking, when tasting.