There is no difference between USPS passport acceptance and the Dallas County Passport acceptance here....none at all. The cost is exactly the same. The speed of receiving the passport is the same... The requirements are exactly the same. There are more USPS locations which accept passport applications..... However, here, all USPS locations around Dallas are booked 4 weeks out. I found an open slot at a small Dallas County passport office about a week after my wife's oath ceremony..
The only difference was the place to book online.