It's not a Rangpur -- we have one of those, and they are extremely sour. Morton includes them in her section on Rangpurs, but they are different.
As for Taiwan, the problem with identifying it is that many Asian tangerines basically look like this. You might be right, but I'm also hoping that someone with experience in Guam or Micronesia will appear. Do the taiwanese tangerines have a very loose peel, few seeds, and a weak flavour?