Music from a laptop- on AC or via battery power?


I see that in the digital world, linear power supplies are often touted as offering a lower noise environment. 

Suppose I am using a laptop. If I’m running it off the AC, certainly the switch mode power supply is in action. Am I correct in thinking that if I’m running strictly on battery power that the power supply is at lest as clean as an active linear power supply? Or is there sill a switch mode power supply still actively doing its thing in the laptop? 
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With my MBP I could hear no difference between battery and powered.  There was a near instantaneous improvement in replacing the MBP with a Roon Nucleus.  A much quieter background (lower noise) that let you hear deeper into the music.  I was quite surprised.
@noromance

Thanks- I thought the SMPS was typically in the external adapter-

Fuzztone- well, at least until I move off the MacBook Pro, i would like to do what I can- I turn off wifi and I run it on battery. But I also think you are right- really can’t hear any significant difference, if any at all, plugged in vs battery

Thank You!
Yes. In most cases, the SMPS is in the external adapter which supplies DC to the laptop.