I had this sort of problem in the Philippines for a TV adapter. Due to the extreme heat of the country and the lack of airflow the ac adapter was overheating and the TV would turn off after a certain amount of time. So I had on of those Gel Cooling Pads for a laptop which I was not using. Mine looked like this.
http://www.amazon.com/Heat-Absorbing-Laptop-Cooling-Ice-Pad-Non-Powered/dp/B00G3VRT9K/ref=sr_1_44?ie=UTF8&qid=1460358709&sr=8-44&keywords=Gel+Cooling+Pad+for+Laptop
Anyway I wrapped it around the power adapter brick and rubber-banded it on.
OF course you might use something else but remember you are dealing with power so be careful.