The Power Monitor component uses the internal ADC to measure the voltage inputs. It compares the results against the OV/UV thresholds.
Advantage: High resolution (12-bits)
Disadvantage: Slow scanning rate. Around 150 us per rail.
The Voltage Fault Detector uses a comparator voltage window.
Advantage: Faster scanning rate and response time. Around 4 us per rail.
Disadvantage: Low resolution (8-bits)