The above answers are correct, the regulatory setting on the controller will prevent APs from exceeding any regional regulatory limits.
To answer your question regarding the 28dBm max (23dBm per chain), the AP-275 is a 3x3 AP, which means there are up to three chains. Each chain being 23dBm, the second chain will add 3dBm to the total output, and the third chain will add another 1.8dB. 23dBm + 3dBm + 1.8dBm gives you 28dBm max (rounding up).