Thailand used 220V AC, and the Empress Hotel Chiang Mai has 3-pin wall outlets in the lecture room and 2-pin wall outlets in the bed rooms, like those shown below on the left and the right, respectively.  If the power leads on your laptop and mobile phone recharger have plugs that will not fit both of these wall outlets and you need an adapter, these can be purchased at various shops in the Maya Shopping Mall opposite the hotel.