http://www.overclock.net/t/719397/on-ripple-and-its-effects-on-overclocking The same author as the one who discussed -whine- in my previous link. This guy is an experienced engineer and provides relatively easy to understand explanations.
Points he makes:
1) the kind of voltage fluctuations that might harm the VR circuitry
require an oscilloscope to see or measure.
2) he says:
The ATX specification sets these limits on computer PSU ripple levels:
+12V - 120mV+5V - 50mV
+3.3V - 50mV
+5VSB - 120mV
-12 - 120mV
My
personal preference is to see numbers in or under this range:
+12V - 80mV+5V - 30mV
+3.3V - 30mV
+5VSB - 50mV
-12V - 80mV
Any power supply which has ripple outside of those proscribed by the ATX specifications can and will cause short term hardware damage (over a period of days to months, depending). Anything outside of my preferences may cause long-term reliability degradation and other issues, though it won't damage your hardware in the short term.
edit: that said. the VoltageRegulator circuit on the card is designed to handle voltage that isn't exactly 12v and convert it to the voltage required by the card. Which in fact is -tweeked- all the time by OC'rs
edit2: Copied from an evaluation of the Asus Hero Maximus motherboard sound system (implying smoothing out ripples is the intended job of a VRM and some noise is not unusual in the power)
"Crystal Sound 3. New for this generation is a new dedicated VRM for the audio sub-system. This change eliminates electrical noise from the power supply to the audio controller for more consistent audio performance. ASUS’ internal testing shows a substantial difference in power noise between the old design and the new. The Z170 Deluxe shows a noise level of 44.5mV compared to 134mV on other designs."