No egg white powder as you call it, is powdered albumin or simply egg white dehydrated. Where tartar is a combo of chemicals that in most cases stops what is known as crystalzation of a product, mostly sugar, Most stabilizers are forms of gums or starches that hold the molecules of the mass together. Guava, tapioca starch , modified corntarch etc.
i got one macaroon recipe which ask for egg white powder. Our kitchen do not have egg white powder then the chef replace with cream of tartar. So i wonder is egg white powder also work as a stabilizer.