Some Anchovy Powders are made from freeze-dried anchovy paste, which has a lot of salt in it.
Others are made from dried anchovies, so that the salting stage in making anchovy paste is skipped. The dried anchovies are chopped and mixed with water heated under pressure. The solids strained out, and the liquid is dried. This results in more of an anchovy taste and less of a salty taste -- instead of being 40% salt, they are about 10% salt. However, if you are using it in a recipe where the salty taste was expected, you may need to boost up the salt you are adding.
Anchovy Powder is mostly used commercially, but you can buy it some places and will see some recipes that call for it.
Use 1/4 the amount of powder as you would paste, as flavour is very concentrated
4 times the amount of anchovy paste
Anchovy Powder has a longer shelf life than anchovy paste, as it does not require refrigeration. Store for up to a year in cupboard.