I went from an EVGA 1080 Ti FTW3 to EVGA 2080 Ti FTW3.
I game exclusively in VR with the Oculus Rift.
I saw no appreciable gain in the fps department, but was able to up some graphics settings and maintain same performance I was getting previously with the 1080 Ti.
 
You will certainly benefit nicely from going to a 20x series card from your 780 ( I would not even try VR on a 780), however VR still is quite demanding especially in things like flight sims and racing sims. Hopefully you are overclocking that 4770k, as it really benefits VR. I am running a 4820k at 4.5 GHz.
I would say you will be fine with the 2070 card if you want to save the money.
Yes your PSU should be fine.
 
 

Moving thread to general hardware subsection.