For me white supremacy is usually perpetrated by bullies. Also the cruel imperialists were white supremacists as well. It promoted lynching and terrorism. As a Hispanic, Italians and Irish never really did anything to me (then again they're not white), but Brits, Danes, Swedes, Israelis historically have been white supremacist cultures.
Yes, white supremacy is a terribly racist view in modern society but what must be remembered in this specific question is that Nazism consists of white supremacy, religious supremacy, an apathetic survival of the fittest policy and a lot more. In a situation where a white supremacist or a Nazi sets up a concentration camp, more people would be oppressed by the Nazi, including certain whites whom are deemed useless (cripples, anti-fascists, etc.) It can simply not be argued that a white-supremacist is more evil than a Nazi because the Nazis are more racist, more discriminatory and offensive to more people.
Nazism took lives of several million people by building concentration,working and death camps to literally destroy the Jewish race. In white supremacy, the idea was that European Americans were better than any other race,and the actions to back up the idea. Not all white people felt this way, but if you were a Nazi you did. One last thing: Jews were horribly treated by the Nazis that they would stoop so low as to give them unsanitary living conditions, little food or water and kill them for so much as looking at them wrong. White supremacy didn't always support those methods of evil.
Yes, White supremacy is a disgusting thing, but Nazism was even worse. With its doctrines of Aryan supremacy and the application of its political platform to justify the killing of 11 million people, Nazism proves to be much worse than white supremacy. While White supremacy is racist and discriminatory, Nazism was the ultimate form of murderous loyalty to a cause.