Vietnam's education system is a complete shit show. Teachers earn scraps leading to a semi-open practice of education related bribery. Resources are all but nonexistent and invariably outdated. Native teachers tend to be poorly educated, whereas foreign teachers are a mix of sexpats and backpackers. And I'm not entirely sure what you are trying to imply with their government, but the nation is not communist. It has a single authoritarian party that oversees a market economy. The only semblances left of communism are an extremely poor people and the complete lack of any freedom of speech. Schools in many cases are practically falling down.
Regardless, the nation somehow is producing even more capable students than the US. When I was young I also went to a incredibly poor urban school. And I also had numerous Vietnamese individuals in my classes who I remain friends with to this day. In an interesting coincidence they too, in spite of enormous adversity of our youth, went on to all do well more than fine. Of course that's completely anecdotal. In looking for demographic data I was completely unsurprised to see Vietnamese well above the median in terms of US median household incomes. [1]
So what's their secret sauce? Whatever it is, it's unlikely to be replicated by just throwing money at the problem anymore than you would manage to turn lead to gold with good intentions and lots of dollars.
[1] - https://en.wikipedia.org/wiki/List_of_ethnic_groups_in_the_U...