can you use meringue powder instead of eggs, to make a cake?

Using meringue powder instead of whole eggs will not give you the same result. Merinue powder is missing the fat of the egg yolks.

If might work for an all egg-white cake, but fresh whites will give you much better result.

meringue powder also has other ingredients besides just egg yolks. They do sell powdered egg whites, as well as powdered whole eggs. I've seen them in the baking aisle of my grocery store.