I use a Roon Nucleus+ connected to an Analog Domain DAC1 through USB.
In the early days I thought I heard a difference with the Weiss MAN301 (AES EBU XLR), but during blind A/B testing I really couldn't tell them apart. My initial impressions probably some kind of "USB device with SMPS cannot be good" bias.
BTW, If the Nucleus+ is not connected directly to a DAC (USB) but only acts as a server on the network (Ethernet), the power supply of the Nucleus simply cannot impact sound quality...if one thinks it does, one probably has far more serious issues in his/her power setup.
I'm so satisfied with the Nucleus performance that I'm on the fence whether to purchase the Roon Nucleus LPS or not, if ever it materialises. Nevertheless, it would probably make for good power hygiene so we will see.
I discussed USB / LPS vs SMPS with several electronics engineers active in the audio industry and all pretty much confirmed that the implementation of the USB input circuit, in particular the galvanic isolation, at the receiving part (DAC) keeps out the unwanted stuff to a level where it simply gets lost in the thermal noise of the circuit.
It all comes down to design, implementation (parts) and build quality. Some Switch Mode Power Supplies will outperform Linear Power Supplies which present their own kind of issues.
Those familiar with the Henk Beeckhuyzen channel will have noticed that some of his reviews mention that a well designed product has very little (to nothing) to gain with a third party PS, be it Linear or Switched Mode.
Although I have a degree in electronics engineering (a long time ago, in a galaxy far far away), my talks with these successful and well respected people rekindled my appreciation for the complexity and intricacies of circuit design within a given budget.
As with so many things in life, the reality of circuit design cannot be captured in black or white statements, but is very fluid and nuanced with trade offs and compromises to be made so products can be brought to market from the very affordable to those qualifying as unobtainium.
But as always, trust your ears.
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