Never used either one to make potato soup....always a kettle. Here's my mother's recipe for it that you may be able to adapt.
3 potatoes, peeled & diced
1 med onion, chopped
2 tablespoons margarine, melted
6 cups milk
1 1/2 tsp salt
1/4 tsp pepper
1 tsp chicken-flavored bouillion granules
1-1 1/2 tsp dried oregano
1 1/2 cups instant mash potato flakes
Cook potatoes in boiling water until tender...drain.
Saute' onions in butter in Dutch Oven until tender.
Stir in next 5 ingredients.
Cook over low heat, stirring constantly until thoroughly heated.
Remove from heat, stir in flakes and potatoes.
Hope this helps you out.