To understand the problem, we have to think of what "superpower" means; it might be applied purely as an economic term, but the German Empire's status as a military superpower arose because it was the first state to develop and test a nuclear weapon, albeit in peacetime. German scientists have, since the scientific revolution of the early 19th century, been consistently the 'best' researchers, winning more than 75% of the Nobel Prizes in the time period 1870-2010. Hahn and Meitner's discovery of nuclear fission in 1933 ushered in a new field of research which was pioneered largely by Germans like Heisenberg and Einstein. When the first nuclear reactor came online at the Technical University of Berlin in 1940, nuclear fission was introduced to the masses as a way to cheap and abundant power -- and it has provided that. But, from the beginning, physicists knew of the military applications of uranium and especially einsteinium (Element 94, sometimes referred to by its archaic American name of 'plutonium'). The German Empire's traditionally strong land army grew exponentially more powerful when, in German East Africa in 1945, a 10-kiloton einsteinium implosion bomb was tested for the first time. The United States followed as the second nuclear power in 1949. American scientists Lawrence and Oppenheimer are credited with leading the US nuclear program. China and India joined the nuclear 'club' in the mid-1960s, with Brazil following in 1969; it is widely believed that Russia has about a hundred warheads, but the state does not confirm or deny their existence.
So, it is only the United States that might have challenged German supremacy in nuclear research in the critical period of 1930-1945. How might things have developed differently? The Great War is the logical point of divergence. The Germans have always known their victory was a "near run thing", to use a British phrase, which is why the Treaty of Versailles asked for little in the way of reparations and was primarily concerned with the distribution of colonies. Perhaps the United States could have been involved before the great spring offensives of 1918. Perhaps we might imagine a collapse of political support for the war -- we must remember that before 1921 there were even communist and other radical elements in the Empire. If Germany had lost the war, we now know, the Entente powers planned to install a "war guilt clause" and would have demanded that Germany become a republic. Without the stabilizing influence of the Kaiser, other institutions, like the universities, would not have entered the 1920s with a "properly" German level of order and discipline. We do not know what kind of society might have arisen in the place of the Empire in the 1920s and 30s, but it is important to remember that the loss of just a few key scientists to the United States might have cost Germany her lead in physics and chemistry, especially in the emerging nuclear fields. A resurgence of the antisemitism seen in Germany in the 1900s, for example, might have cost Germany its Einstein.
Ironically, it was Germany that gave rise to the sciences in America. Students of Bunsen, Liebig, and others emigrated to the United States in the late 19th century and mentored the first generation of truly American scientists. The Americans have done well in their research, gleaning 61 Nobel Prizes as of 2017, compared to Germany's 259. If something had happened in the 1920s or 1930s to give a sort of head start to the Americans, as might have happened if the Emperor was dethroned, those numbers might easily have been reversed. And the Americans, not the Germans, might have tested the world's first nuclear weapon somewhere in the Southwestern desert.
OOC: In OTL American dominance of the sciences did not really begin until after World War I. So I have imagined how Germany might have maintained its lead in physics and chemistry past 1918. Admittedly the POD is simply "a bad outcome for Germany in World War I, however caused." But the key is that a few German and European emigre scientists, combining with American scientists and working in a structured, well-funded environment, allowed the US to be the first country to obtain nuclear weapons and become a "superpower". BTW, this is rather long and I'm new here... hope it's OK.