what is the gtx 780 2048mb

Obviously, fake. At flea markets full of these, so you need to be very careful not to fall into this trap.

there are only 3 and 6 GB. the latter sort of ti.
there is a possibility that the card is executed and it is thus fixed turning blocks leading to the uncorrected point.
but most likely someone just enters to pitch sublicensee

MunchkiN 616
Maybe it's cheap Chinese modification of the GTX 650. Often now I see the cards say 780 with the characteristics of the previous models. Enough to slightly tweak the BIOS of the SE, a bit to disperse and all. Standard Chinese practice.