I would hazard a guess that when you use it from battery you are not getting all the and RFI from the mains supply.
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It’s well-known that a laptop is a noisy source. More noise gets added when powered by an AC/DC wall wart - which is a cheap switch-mode power supply. Running on the battery is far better but doesn’t last long. A quieter option is to get a regulated linear power supply (LPS) - something like this one - and plug it into a power conditioner/filter. Find out what DC voltage your laptop uses.
I personally use a mini Linux PC plugged into the wall, with my audio plugged into a Furman. This keeps the PC supply outside the Furman's noise filtering.
Also, in addition to the switch mode noise, there's been evidence of ground loops occuring ONLY when the AC supply is plugged in and a metal cable is used. Modern USB capable dacs should be galvanically isolated, but this may not always be the case. It is worth experimenting with USB isolators or optical connectors.
Just to add a litte. Usually when there is a ground loop in analog, we hear it as a hum. According to some old measurements from Stereophile, you could have a ground loop via USB which does not cause a hum but instead results in excessive jitter.
Unfortunately, Stereophile decided then to stop measuring with laptops plugged into AC outlets. IMHO, they should have kept testing with AC to encourage manufacturers to fix the problem.