Jupitah :
what is a dac? sry for being a noob...
FYi my card is a GTX 760..
Digital analogic converter, DVI is a digital signal while VGA is an agalogic signal, the dvi-to-vga adapter is only a "adapter" that use the DVI pinout of the card to give a vga analogic signal from the card instead having two diferent connectors just allow to use the same.
As you would convert from digital to analogic on the card, that conversion could affect image quality as in some cases affect also the quality of the image the components between the conversion and the monitor (card components like capacitors of output filters) or other ouside factors like vga cable quality and lengh, parasit, interferences on the vga signal due closer power wires, etc...
On DVI is easier as you transmit digital information to the pannel, only original image quality settings (like Nivida using lower than optimal colour pallete of 16-235 instead 0-255 on HDMI output signal) and proper monitor factors have effect on the image.