Peel and slice the potatoes into thin slices.
In a large bowl, whisk together cream of mushroom soup, heavy cream, chicken broth, sour cream, garlic powder, salt, pepper, and 1 cup cheddar cheese.
Add potatoes into the cream mixture, and mix.
Add the potato mixture to the instant pot.
Seal the lid and cook on high pressure for 2-3 minutes.
Allow a 1 minute natural release, then perform a quick release.
Stir gently and add remaining cheddar cheese and parmesan cheese.
Use the sauté function for 2-3 minutes if needed to thicken the sauce.
Optional: transfer to a baking dish and broil until golden and bubbly.
Let rest 10 minutes before serving.