I think most democratic nations have a similar principle of separation of powers, so... almost all of them?

The US is rich because it's well functioning.

The US is rich for many reasons that have little to do with being well governed.

* The country was launched on most of a century of essentially "free" land grabs-- limited pushback from native civilizations. buying cheap from distressed foreign powers (Louisiana), the main wars of conquest being insignificant squabbles with Mexico over trifles.

* Said land was also compelling-- you weren't fighting the environment to extract value the way you would be in Siberia.

* After 1865, no significant nation-scale conflict on the territory itself to blow down existing investments.

* This created an opportunity for bulk immigration-- first with Homestead Act style programmes and then because the American economy was compelling enough to be a pull by itself. A high immigrant population has a unique "opt-in" demographics-- a situation that self-selects for entrepeneurialism.

None of this required wildly competent government. George Washington could have chosen to be a king, a religious caliph, or a protosocialist planning enthusiast, and the deck would have still held almost all the same cards.

Name one and detail how the administrative state differs