Applies to: UD-3900PDZ only, reviewed 12 September 2026. Output, software, OS and power-revision qualifications are not transferable to UD-6950PDZ or UD-ULTC4K.

The three HDMI sockets do different work

OutputTechnologyDocumented ceiling
HDMI 1Native USB-C DisplayPort Alt Mode3840 × 2160 at 30 Hz
HDMI 2DisplayLink DL-39001920 × 1200 at 60 Hz
HDMI 3DisplayLink DL-39001920 × 1200 at 60 Hz

The two software outputs also cover 1080p60, but not 1366 × 768. This is an office/productivity arrangement, not triple 4K60. Plugable: UD-3900PDZ output-specific specifications

Functional connection map

USB-C / USB4 / Thunderbolt computerIncluded 0.84 m USB-C 5Gbps cable → rear host portPlugable UD-3900PDZ
  1. HDMI 1 · nativeDisplayPort Alt Mode through host linkdisplay 1, up to 4K30
  2. HDMI 2 · DisplayLinkUSB graphicsdisplay 2, up to 1920 × 1200 / 60
  3. HDMI 3 · DisplayLinkUSB graphicsdisplay 3, up to 1920 × 1200 / 60
  • Power90 W supply / 60 W host on old units; 135 W / 100 W on new
  • DataOfficial page conflicts: detailed inventory says 6× USB-A; another section mentions front USB-C—inspect the exact unit
  • OtherGigabit Ethernet + front 3.5 mm TRRS
Functional connection map—not physical socket positions. The rear label sets the charging revision. HDMI cables are user-supplied.

Read the charging label before comparing power

Units made before January 2025 provide up to 60 W from a 90 W supply. Updated units provide up to 100 W from a 135 W supply. Other setup and port behavior is unchanged. The shared model name alone cannot establish charging. Plugable UD-3900PDZ: 60 W and 100 W revisions

What the desk needs: cable and software paths

ItemDocumented starting pointWhy it changes the result
Host cableIncluded 0.84 m USB-C-to-USB-C 5Gbps cableA replacement must carry USB data, USB-PD and DP Alt Mode; charge-only cable or USB-C-to-A cannot preserve HDMI 1 native video.
Display cablesBring one HDMI cable per displayHDMI cables are not listed in the standard box.
Windows 10/11DisplayLink normally arrives through Windows UpdateHDMI 2/3 need working DisplayLink; HDMI 1 does not.
macOS 11+Install, run and permit DisplayLink ManagerWithout it, native HDMI 1 can survive while HDMI 2/3 stay absent.
ChromeOS 100+Built-in DisplayLink support; keep ChromeOS currentPlugable does not recommend this DisplayLink dock for Linux.

Plugable: UD-3900PDZ output-specific specifications · Plugable: current DisplayLink downloads and OS notes

Set up in an order that isolates both paths

  1. Prepare current DisplayLink support for the operating system; macOS also needs the Manager permission.
  2. Power the dock and connect the included cable from the rear host port to a computer port with USB data, DP Alt Mode and USB-PD input if charging matters.
  3. Put the highest-resolution screen on HDMI 1. Select its input and verify the native path.
  4. Add HDMI 2, then HDMI 3, using one cable per display and supported modes.
  5. Arrange extended desktops, then add Ethernet, audio and USB devices. Check their results separately.

Recover from partial success

Observed resultLikely branchNext controlled check
HDMI 1 works; 2 and 3 are darkDisplayLink softwareRestore/update the driver; on macOS allow and enable each DisplayLink screen.
HDMI 2/3 work; HDMI 1 is darkNative Alt ModeConfirm the computer port supports video and test one known-good HDMI cable/display.
After Apple-silicon restart/wake, HDMI 1 and charging remain but HDMI 2/3, USB, Ethernet or audio disappearDocumented USB-branch recoveryDisconnect host 10–15 seconds. If needed, disconnect host and AC, fully shut down the Mac, wait 60–90 seconds, boot, wait 30–60 seconds after login, restore dock AC, then reconnect host.
No blue power lightOutlet, revision-matched 90 W/135 W adapter and AC leadRestore dock power before changing display software or host settings.
Blue light on; no dock functionsSupplied host cable, rear laptop port and computer USB-C portAC is present; host-link and cable diagnosis is now isolated.
Network links but is slower on macOSDriver/OS limitKeep actual throughput separate from the Gigabit port label; Plugable notes about 100–300 Mbps may occur.
No chargingPower revision / host PDConfirm the rear label and computer’s PD input; use its own charger too if needed.

Plugable UD-3900PDZ: Apple-silicon restart and wake recovery · Plugable: using the laptop charger with a charging dock

What remains unknown or conflicting

A stale requirements block on Plugable’s page names a different product and implies 4K60; the exact UD-3900PDZ output table caps HDMI 1 at 4K30. The same page’s detailed inventory lists six USB-A ports while another section mentions a front USB-C port. Inspect the exact unit; this guide promises neither downstream layout. HDCP and protected playback are not a safe assumption.

Sources & scope

These instructions combine published references with our proposed diagnostic sequence. This setup has not been physically tested by Connect Your Dock. Manufacturer documents can change; use the exact model and scope linked below.

How we assess evidence