My ups gives me per port and combined total consumption via the management interface. So I'll plug one in, check the draw, and then plug in the second, give it a few minutes to balance, and then check it again.
I'm going to test this once I have everything plugged in. (I'll have 27 RJ and both SFPs in use once I get my 3 x 2 port NIC cards for my server (DCS C6005)).
Obviously it's not going to be 100% accurate, but if should give me a decent idea if the efficiency goes up/down with single vs dual PSU's. My guess is that most PSUs (especially enterprise class PSUs) are not gold/platinum rated (at least I doubt the ones on these Quanta's are), so their efficiency point is usually around 50-60% power draw. With a single PSU, I'd suspect the efficiency point is probably lower, and based on the consumption I'd think the single PSU will be out of its efficiency point (so it has to run hotter for the conversion). With a second PSU, I'd guess that both can sit well within their efficiency point and be actually consuming less power, since they don't have to lose conversion power to heat.
I'm purely speculating of course, I'm curious if I can get accurate enough readings to see if I can detect a benefit of dual vs single.
I'm also curious if there is a way to "disable" the switch from knowing that it HAS a second PSU option (I'm sure the versions that only come with one PSU don't run in "emergency" mode with only a single PSU). It would be interesting to see if I can figure out how to "disable" the second PSU completely, to prevent the fans/etc from running in full power mode when not needed.
Can anybody tell me if the chassis fans are PWM based?