As luck would have it, I was in Hsinchu City today and I was looking for these places to give you the locations.
It appears that the Cal-Mex place is gone. I could not find it. It used to be on Guangfu Rd between NOVA and Starbucks. Funny enough, Starbucks is gone, too. I thought you couldn’t kill them nuclear radiation!
The other place is actually called “Taco House” and it is on Sanmin Rd, Lane 3. No. 13. How to get there, assuming you are driving, is to go west on Dongda Rd from Zhonghua Rd. You will see it on your right. I have included pictures. Sorry, no guac on the menu, most likely for the previously discussed expense of avocados. I cannot personally speak for the meat side, but from what I am told the meat tacos, etc are spot on for Taco Bell. They even have tator tots!! I grew up in Wyoming, we had a place called Taco Johns, a sad TB knock-off. They had tator tots and called them something else…too old, cannot remember.
The vegetarian versions are simply meat versions minus the meat. So, using that measure, do not get your hopes up too high. As mentioned in this thread, there are two ways to get something in Taiwan, or anywhere. Take what you can get, or do it yourself. Anyway, enjoy the pics and menu.