There are two major effects of China’s increasing prosperity on the relationship between that country and the US. First, the rise of China allows China to be more influential around the world. Second, it allows China to be more aggressive and confrontational in its interactions with the US.
Because China has become more prosperous, it is able to try to project its influence farther around the world. It is trying to be more of a regional power while also trying to project economic influence into places like Africa. This tends to complicate its relations with the US because it puts China into more situations in which its interests may compete with those of the US.
Because China is more prosperous, and because it appears to be rising while the US is struggling, it is willing and able to be less deferential towards the US. China no longer feels like it is dealing with the US from a position of weakness. Therefore, it is much more likely to push hard against the US in instances where the two countries do not agree.
In these ways, China’s increasing prosperity has made its relationship with the US much more contentious.