When traveling with meds, always keep them in their original containers and carry a copy of the prescription and/or doctor's letter. Always in carry-on, never checked baggage. That's just general travel practice, not specific to Taiwan.

Xanax and Paxil are both legal in Taiwan when prescribed by a doctor, so there should certainly be no problem whatsoever over a few day's worth. As other posters have said, they very seldom stop anyone who looks remotely like a Western businessman or tourist at TPE customs--you just look straight ahead and walk out--, and even when they do, they are professional and quick.