delta-sigma dac
Both dacs need "mixed-signal" processes since the output stages need analog post processing!
while pwm vaires the pulse width of the output linearly to the digital input (V_out rms ~ V_in_digital) , a sigma-delta dac has a more complex signal processing. the quantization noise of the pwm dac is constant over the whole spectrum, while due to (sigma-delta) noise-shaping signal processing most of the quantization noise is shifted out of your signal bandwidth (oversampling required!). Therefore the SNR is better as for pwm for same power dissipation and convertion rates. another benefit over the pwm consists in good DNL and INL compared to the pwm dac.
in both cases, the output of the dacs are filtered (passive or active) afterwards in order to supress the "high frequency" noise.