Probably the best-known non-Italian 'ethnic-based mafia' that operated in the USA was the Unione Corse.
This group were not North-European, but were part of the Corsican Mafia and maintained the so-called French Connection monopoly, controlling the import of Heroin, from French Indo-China, through France (and Canada) into the United States from the 1930s until the late 1970s.
The Irish organised crime groups that operated from the nineteenth century onwards are another well known group that might be classified as an 'ethnic-based mafia'. Sometimes collectively known as the "Irish Mob", this group actually originated in the Irish street gangs in the United States.
Those gangs were made famous (or, perhaps more accurately, infamous) by Herbert Asbury's 1928 book The Gangs of New York, which was loosely adapted into Martin Scorsese's 2002 film of the same name. As a group whose members are linked to a North-European country, this might meet your requirements.
In this case, the Irish Mob appears to have originated in the US in the nineteenth century and then expanded back into Ireland at some point in the 1960s. This growth of organised crime in Ireland was the subject of the 3-part documentary series Bad Fellas on RTÉ Television.
Although operating on a smaller scale, the so-called "Polish Mob" are another North-European 'ethnic-based mafia'.
Some well-known elements include the Saltis-McErlane Gang in Chicago, the Kielbasa Posse in Philadelphia, the Greenpoint Crew from Brooklyn, the Flats Mob in Cleveland, and the The Flathead gang in Detroit.
As for your specific question about German or Prussian mafias operating in the United states, I have to say that I haven't found any references to a significant 'German mafia' or 'Prussian mafia' operating in the United States.
I did find this post on Reddit that also seems to suggest that, while it seems likely that there were some German criminal groups active in the US, they didn't operate on the same scale as some other groups:
I've researched and written about the early years of the Mafia in the US, and looked at Jewish and Irish organised crime in New York as well, I have never come across any references to a German equivalent. This is not to say it never occurred – and in fact, given that at least 6 million German emigrated to the US during the 19th and early 20th centuries, I'd be very surprised if it never did – but certainly Germans were not as prominent as other ethnic groups in organised crime.
Finally, it is worth noting that Wikipedia maintains a list of '"Criminal enterprises, gangs and syndicates", which includes a (presumably not exhaustive) list of gangs operating in the United States.
Included in this list you will also find the Jewish-American organised-crime groups that were active in the United States in the late nineteenth and early twentieth centuries, and which are not infrequently referred to as the ' Jewish Mafia' in the media and popular culture. Some members of these groups did have German ancestry.