With a POD of 1600 how can China have become the preeminent Superpower of the 20th century ahead of the US and USSR?
Revolt of Three Feudatories, with help of Tungning Kingdom, topples the Qing, or at least drives them back to Manchuria. After Wu Sangui's death, his realm does not have a stable succession and the Tungning regime grows in power in Taiwan and then the southeastern coast as the heirs of the Qing and Feudatories fragment. Tungning is also more influenced by western ships, arms and religions.
Eventually, they install a neo-Ming regime over China that is heavily Catholic influenced, and merges eastern and western concepts of empire and mercantilism. It's fleets establish a Monroe doctrine over Pacific trade and then Indian Ocean trade.
With a POD of 1600, the US and USSR probably don't even exist.
But Russia exists, and probably expands into Asia until it runs into China's interests (which might themselves expand more, or might not).
And an Anglo-America has a decent chance of coming into existence. Though England's colony was lost and not yet refounded in 1607, the English had named and claimed Virginia. They were on track for the global commercial ambition and internal religious strife of the 1600s that shaped their American colonization.
So no USA or USSR, but maybe a *USA* or *USSR* doppleganger/counterpart of sorts.