Power Adapter getting scorching hot

keep it off soft surfaces (like beds & lounges)

Being you have overclocked your graphics card your drawing more power than the stock system.

ASUS normally have a 19v DC power adapter somewhere around 3.5-4 amp
you can look at getting an aftermarket power pack that is rated higher than the stock adapter and will therefor run cooler.

YOU MUST KEEP THE VOLTAGE EXACTLY THE SAME
the Amps you need atleast what the orgional had but you can go as high as you like as the laptop will only draw what it needs to run.

so if ur laptop draws 3.9amp and you have a 4.5amp adapter it will only draw 3.9 meaning the adapter dosnt do as much work and will run cooler

or just turn your Video card back to stock.

Acctually, It's very normal the adapter will get hot especially when your laptop is running up. But usually not that hot as you said. I strongly Suggest you get a new adapter. I have this problem before, and I got a new one from RAVPower. It's little hot sometimes, basically works fine. Another thing is you should have a good ventilation environment when you use your laptop.