Meringue powder substitute? Powdered egg whites?

Ive used powdered egg whites for royal icing (that calls for meringue powder) just fine. Meringue powder has sugar in it. Since you use powdered sugar in royal icing, it's fine.
You can get meringue powder at Michaels or some other craft stores that sell cake decorating supplies.

I'm pretty sure I've used both in the past with equal success.