Yoommo

EarStudio ES100-24bit Portable High-Resolution Bluetooth Receiver/USB DAC/Headphone Amp with LDAC, aptX HD, aptX, AAC (3.5mm unbalanced & 2.5mm balanced output)

AudioQuest - DragonFly Red USB DAC/Headphone Amplifier

FiiO A3 Portable Headphone Amplifier (Black)

Listen up Personal Sound Amplifier

CHORD Electronics Mojo, ultimate DAC/Headphone Amplifier, USB, Coaxial, and Optical, Black

iFi Audio Nano iDSD Black Label Portable DAC and Headphone Amplifier

VOZA (Regular $59.99) V100D [XBASS] Hi-Res Dual-Drivers in-Ear Headphones (75% Off Now Till 8/15)

Creative Sound Blaster X7 High-Resolution USB DAC 600 ohm Headphone Amplifier with Bluetooth Connectivity

VANMASS 2-in-1 Lightning Adapter, Lightning to 3.5mm Audio Jack Lightning Charging Port AUX Splitter Compatible iPhone 7/7 Plus/8/8 Plus/X, iPad, iPod (Support iOS 11.4 Previous)

Pyle-Pro PHA40 4-Channel Stereo Headphone Amplifier