Astell & Kern's new USB-C DAC promises hi-fi audio for phones without headphone jacks - The Verge
Amazon.com: AudioQuest DragonFly Black v1.5 Plug-in USB DAC + Preamp + Headphone Amp : Industrial & Scientific
Amazon.com: FiiO K3 DSD256 | 384K/32Bit USB-C DAC and Headphone Amplifier for Home and Computer(3.5mm Single Ended/2.5mm Balanced/Coaxial and Optical Digital Outs) (K3 Titanium) : Electronics
Shanling Audio UA2 Portable USB DAC AMP Review: This $85 Dac Amp Combo Has Jaw-Dropping Power and Sound! - HIFI Trends
Headphone DAC/amps: The best way to enjoy lossless audio | Digital Trends
Amazon.com: FiiO K3 Type-C USB DAC Headphone Amp : Electronics