- Elecrow AUS50024E (1920x1080 or 2560x1600 HDR, 10.1") they have a big selection, visit their website. They make no mention of this working with Dex but do say:
Works perfectly for PS3, PS4, WiiU, XBOX360, Raspberry Pi 3, 2, & 1 Model B or B+, industrial equipment, car audio and video, car headrest, medical equipment display.
- The GeChic 1503E Monitor (1920x1080, 15.6") specifically mentions that usability with smartphones is one of its abilities:
Enlarge Your Mobile Phone without Sacrificing Quality
On-Lap 1503E is always your smartphone’s perfect match. Make sure your smartphone supports HDMI output and use the manufacturer’s adapter to output your mobile phone to On-Lap 1503E.
The GeChic 1101P Monitor (1920x1080, 11.6") has HDMI, and DisplayPort, it mentions it works with a Mac, no mention of smartphones, uses a battery pack (which is probably better than USB powered).
The GeChic 1102H Monitor (1920x1080, 11.6") has built-in battery that they claim lasts 4 1/2 hours.
See also: "10 Best Portable Monitors".
It is also possible to use Moverio BT-300 glasses which simulate a 40" (at 2.5 m) or 320" (at 20 m) screen, they're U$800 but don't need a Dex; they can also be used to fly a drone (if that recoupes some of the cost).