The answer is yes - the card will work in another system.  It's becoming very common for buyers to select pre-built systems just for the video card -- since the current shortages mean  buying one separately is either prohibitively expensive or (for some models like this one) difficult to impossible.  
I want to build my own new PC and I am wondering if it's possible to put the DELL Nvidia RTX 3070  from my Alienware Aurora Ryzen in a new PC with a new motherboard?  
Alienware RTX 3070 in a new PC