Fill a large pot with water and bring to a boil; cook the fettuccine according to package directions, leaving the water unsalted.
In a heavy medium saucepan over low heat, combine the butter and cubed cream cheese and warm, stirring frequently until mostly melted.
Add the Parmesan cheese and heavy cream to the pan and continue stirring; whisk briskly if lumps form until the sauce is smooth.
Stir in the garlic powder, cracked black pepper, and dried oregano; keep the sauce over low heat and stir often to prevent sticking, lowering the heat if it begins to cling to the pan.
Taste the sauce and season with salt if needed; to check final seasoning, dip a cooked noodle into the sauce and taste the combination, then adjust salt and pepper to preference.
Drain the cooked fettuccine and transfer to a warmed serving dish or back to the pot, pour the sauce over the noodles, toss gently to coat, garnish with fresh oregano, and serve immediately.