By the way, if you want to have one condiment that only people in Taiwan use a lot and rarely used by anyone else, this is a good place to start.
It’s supposed to be the Satay sauce commonly used in SEA cuisine, hence the Taigi name for the sauce, sa-tê, but tastes nothing like it. You can use it as a barbecue sauce, but it’s more commonly used as a dip for your hotpot, usually with soy sauce, scallions, and if you are brave, a raw egg. People also stir fry vegetables, noodles, or rice with it.
This sweet and spicy sauce can be bought at 99 Ranch. The Dragon Boat Festival is coming up, and it’s the traditional sauce to go with the glutinous rice ball dish called zongzi.
Taiwanese black vinegar, which is often added to soups, especially the kinds with starch added at the end to make it a bit thicker.
If you are up for anything, the next 2 items infamous to non-natives can be found in pretty much any Taiwanese pantry.
This one is often called pork floss. You can eat it with rice, put it on porridge, in sandwiches, buns, wraps, Taiwanese people pretty much put it in anything.

This is called fermented tofu. People would eat it as a spread on white buns or in porridge, often together with pork floss. You can also stir fried vegetables like kangkong (the vegetable with a hollow stem) with it.
Make sure you only buy products made in Taiwan, as stuff made elsewhere, especially in China, could taste very different.