Bring a large pot of water to a boil and cook the fettuccine according to package instructions, leaving the water unsalted as directed.
While the pasta cooks, place the butter and cubed cream cheese in a medium heavy-bottomed saucepan over low heat and melt, stirring frequently.
Add the Parmesan cheese and heavy cream to the melted butter and cream cheese, stirring constantly; whisk vigorously if lumps form until the sauce is smooth.
Stir in the garlic powder, cracked black pepper, and dried oregano; continue to cook over low heat and stir often to prevent sticking, lowering the heat if the sauce begins to cling to the pan.
Taste the sauce and add salt if needed; dip a cooked noodle into the sauce and taste the noodle plus sauce together to ensure the seasoning is balanced, then adjust salt as required.
Drain the cooked fettuccine, return it to the pot or a serving bowl, pour the sauce over the noodles, toss gently to combine, garnish with fresh oregano, and serve immediately.