Place a heavy medium saucepan over low heat and add the butter and the cubed cream cheese; cook, stirring frequently, until the cream cheese is softened and beginning to melt.
Add the Parmesan cheese and heavy cream to the pan and stir continuously; whisk briskly if lumps form until the mixture is smooth.
Stir in the garlic powder, cracked black pepper, and dried oregano; keep the heat low and stir often to prevent sticking, lowering the heat if the sauce begins to cling to the pan.
While the sauce is warming, bring a large pot of water to a boil and cook the fettuccine according to package instructions, leaving the water unsalted as directed.
Taste the sauce and add salt if needed (Parmesan is salty, so it may not require much). Dip a cooked noodle into the sauce and taste to confirm the combined seasoning, then adjust salt as necessary.
Drain the pasta, return it to the pot or a serving bowl, pour the hot sauce over the noodles, gently toss to coat, garnish with fresh oregano, and serve immediately.
