External Switch Mode Power Supplies are included with many headphone amps as a way to keep cost and shipping weight down, except Schiit which use external transformers with true Linear Power Supplies internal to the chassis in their lower cost products. SMPS offer higher efficiency, less heat, smaller size and weight. Unfortunately they often have higher residual noise which does affect amplifier performance. SMPS vs. LPS effect on an example headphone amplifier may be found here: SMPS vs LPS effect on Garage1217 Project Sunrise III The following single massive stage LC filter will reduce SMPS residual ripple and noise. Parts cost was approximately $42 US in component single unit quantities, and about 2 hours of construction time. It will work with any external SMPS or LPS between 1 and 48 VDC with current less than 2A. Examples include Garage1217 and the Massdrop Cavalli Tube Hybrid (MCTH) headphone amps. Component values were chosen to achieve greater than 20 dB reduction at 60 Hz with greater than 60 dB reduction at 1000 Hz. Here are the Linear Technology Spice simulations with various dB vs. frequency noted: Noise reduction at 60 Hz Noise reduction at 1000 Hz Noise reduction at 10 KHz Noise reduction at 75 KHz Measured performance Meanwell GS40A24-P1J - 24Vdc with 430 mA resistive load Meanwell GS40A24-P1J + Noise Nuke LC filter - 24Vdc with 430 mA resistive load SMPS noise has been nuked substantially. Linear Power Supplies may also have residual ripple and benefit from the Noise Nuke LC filter. Jay's Audio Talema LPS - 24Vdc with 430 mA resistive load Jay's Audio Talema LPS + Noise Nuke LC filter - 24Vdc with 430 mA resistive load Keysight U8001A will have lower residual noise but is also rather large, heavy and expensive; currently approximately $440 US. The Jay's Audio Talema was $115 US at the time I acquired it. $42 US for the Noise Nuke plus several hours construction time to achieve nearly the same performance in a much more transportable format is a good tradeoff for me.