DAC: Vcc or Vref determine resolution?
Resolution for ADC/DAC could be estimated by LSB (Least Significant Bit) i.e given by:

$$ LSB = \frac{V_{ref}}{2^N} $$, where \$ N \$ is number of bits. But these are for architectures that use voltage for conversion, there are architectures that use current then this may not hold true.