[1] - https://en.wikipedia.org/wiki/International_Emergency_Econom...
[2] - https://en.wikipedia.org/wiki/List_of_national_emergencies_i...
Sanctions are crystal clear thanks to the IEEPA [1]. The president needs only declare an emergency, which is typically done in the exact same executive order imposing the sanctions. We're currently under at least 42 different national "emergencies", of which 34 are to impose sanctions. [2] The legal basis for tariffs is less clear, but in effect no different. Trump's tariffs [3] were all passed unilaterally, appealing to all sorts of acts that grant the president conditional tariff powers, but where the condition is framed in a broad enough way to include nearly any rationale.
[1] - https://en.wikipedia.org/wiki/International_Emergency_Econom...
[2] - https://en.wikipedia.org/wiki/List_of_national_emergencies_i...
In China, Xi can decide to impose tariffs or sanctions, and there's nothing anyone can do about it.
The NPC has immense power. They can override anything Xi Jinping does, and even have the power to completely recall him, or amend the constitution. But of course this won't happen. They have a one-party system with relatively minimal internal conflict. So even though the NPC is genuinely powerful and has every check and balance imaginable, they will not be using them.