Hey Painterspal,
At the risk of sounding conflicted, I have to say I am still very intrigued by your findings. It's just that I was troubled when I saw a post asking if the Meridian Explorer wouldn't sound good without the external power supply. I just want to make sure everyone sets their goals first - portable operation vs. desktop operation.
I am, nevertheless, a clean-power freak and don't doubt for a minute that you are hearing obvious improvements when willing to be tethered to an AC outlet. And I can even embrace the possibility that all USB power is dirty to some degree - as you have argued. So, I'm very appreciative of your impressions, while remaining steadfast in reminding people that they might not have the same experience as you have, when willing to use the Meridian Explorer as a desktop DAC on external AC power.
Indeed, Michael Lavorgna (www.audiostream.com) wrote that after hearing great improvements using the iUSBPower with his Audioquest Dragonfly, he said he was surprised to find that he heard no improvements when using it with a different USB-powered DAC on the same PC, same USB port. So... there are a lot of variables here, including the "power-cleaning" capabilities of the portable DAC itself, at which I believe the CEntrance DACport LX, excels, for example.
Ultimately, as with all audio gear, no one can know with certainty what they're missing, if anything, without buying or borrowing a component, to test in their own equipment chain. I don't hear any noise problems (or lack of micro details) with my USB-powered DACport LX when comparing it to my AC-powered DACmini CX (with my laptop, my headphones, my ears). I remain, however, very curious about the possibility that a $199 external power supply could make a difference with my DACport LX, but I'm not willing to spend the money to find out - I'm content for now.
That said, for someone who doesn't own an AC-powered desktop DAC, but wants a portable DAC to do double-duty, the iUSBPower seems like a worthwhile experiment.
Thanks again for your very credible comments!
Mike