With a retailer (Best Buy, etc.) yes.  With Dell, no.  Systems are not built by Dell - they are built in China (notebooks and desktops) or Mexico (desktops) and shipped direct to retailers or consumers;  Dell does not stock pre-built hardware.  
Per this 2017 thread, it would be great to walk in and leave one computer for repair and purchase another (placing the order in advance, of course). Is this possible?
Dell headquarters, walk in requests? #3