Those three powders alone don't make compost. For compost, you need to compost a wide variety of materials. Having just a few ingrediants doesn't make good compost. You can definately add those to compost and potting mix to make better potting mix, but you can't just use those three alone to make dirt into good soil. The three big nutrients everything thinks are important, N-P-K, aren't always as important as the micro nutrients, like iron zinc, etc. You want a good even mix of all nutrients, with few shinning over the others. Basically, you should research your plants and find out what they wand, and adjust your dirt/soil to each plans needs. Usually a good compost will cover just about all plants.
Home Gardener from Austin, TX; by way of Iowa.