I understood that he used a laptop instead of a desktop, but I could be mistaken, often am.
Laptop or desktop, the way he described his power source was:
which is to say, it's at least as dirty as any USB power source you could come up with. And, even with the dirtiest source of USB power, he measured a SINAD of 112dB. Either you have golden ears, or the difference between "dirty" and "clean" 5V power supplies is inaudible.