Well it is going to get more and more informal ofcourse, but I am sure everyone will understand "plug the cord into the wall" or just "plug it in". It is a question of style imo, depending on how (in)formal you wish to be.
Can you plug it into the Wall --- understood by most to be a cord of an electrical device to be connected to the electrical outlet, but syntax-wise it it doesn't quite cut it in my opinion as the wall doesn't generate power.
Can you please plug the cord to the outlet ? - This is the most natural. When you have a vacuum cleaner out for some cleani