What should I do if the embassy asks for supplementary materials after the US visa interview is passed?

Don't worry, since it's over, you don't need to sign it yourself. It's just that the visa officer didn't see your SEVIS fee receipt when you signed it in person and didn't dare to give you a visa, so he asked you to supplement the materials. Because according to their regulations, you must see SEVIS' receipt before issuing you a visa.

I can usually pass. Don't worry, just wait. The embassy will put your passport on the visa and return it to China CITIC Bank where you left your passport, together with a copy of the receipt of the SEVIS fee you paid. After receiving your visa and passport, CITIC Bank will call or email you to collect it. The specific time required for this process is slightly different according to the distance between the embassy where you face-to-face sign and the CITIC Bank where you reserve your passport. But only for a few days.