Apple or Samsung USB-C dongles are fine, but on Android phones they require some fiddling in UAPP every time you connect them to get the volume limit removed.
You can do this for free (UAPP Trial works to unlock the volume), but it's a nuissance.

Also, the Samsung dongle is impedance-sensing, which means it slightly reduces maximum output voltage if you connect low impedance headphones, like K702 or the planars.

So I recommend something like Tempotec Sonata HD II, because it is using one of those ESS chips that have 2V output and do not care for headphone impedance.