Sure, they make plenty of powerline adapters that also act as a wifi access point on the remote end. Ethernet cable from your downstairs router to the wall outlet; wireless comes out of the adapter in the upstairs wall outlet.
http://www.amazon.com/Netgear-Powerline-500-Wi-Fi-XWNB5221-100PAS/dp/B0111MRE68/
A lot of them also have an Ethernet output on the remote end, and it's probably wise to have that in case the wifi directly from the adapter isn't working as well as you'd like. THEN you can plug a router into that Ethernet connection and set that up for your wireless upstairs.