Just a heads up... I'm not
surprised, but was curious to know how this would be handled.... Now I know.
If you have a PCB assembled by JLCPCB but require a component that has to sourced from the USA (Mouser, or your own parts shipped to JLCPCB, for example) the cost of that component will be factored into the import duties... even if you've already paid for the component.
So if, hypothetically speaking, you were to have $1300 worth of THAT4305 IC's shipped to JLCPCB to be soldered onto PCBs you would have to pay an additional ~$750 in tariffs when those IC's come
back into the USA.
The real kicker is that it doesn't matter if the component was manufactured in the USA (which THAT semiconductors surprisingly are), you pay the Chinese tariff rate for the entire assembly.