I don't think the USSR can 'win' the Cold War unless they introduce economic reform a la Deng Xiaoping. Their economic system will fall apart at some point.
The USSR unquestionably would need economic reforms to survive, but that doesn't necessarily have to mean Deng-style pseudocapitalism. However, most of the other possibilities have never been tried on a large scale so there's no way to know if they would work or not.
With a PoD well before WWII, there's a very slim chance the USSR could develop and field mass atomic forces before any of its competitors, leading to a Communist-dominated world. It would require ASBish levels of bad luck and incompetence for their competitors, however. Something like: a non-Hitler fascist comes to power in Germany and gets western Europe embroiled in a war that the Soviets are able to stay out of, that basically wrecks the continent. The US goes isolationist and mildly fascist, so that they're not interested in Jewish refugees, and the Jewish physicists go east to Russia as the least bad destination available. Soviets build and field a few hundred atom bombs before anyone notices, along with an intercontinental bomber force, then use those to enforce a monopoly on atomic weaponry.