Cleaner music when laptop is on battery vs plugged in

Make sure your USB cable from the PC to the DAC has a ferrite core at the PC end, and even better, both ends.

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.

Thank you everyone for the input.
@erik_squires : Which Furman equipment do you use for power filtering? I am looking for a power filter/conditioner but don’t know which one is good. Could you suggest?My budget is $300.

Thank you.