Start with evidence
Run the tests that separate the likely branches
Data Transfer Time CalculatorEstimate ideal transfer time from data size and an entered link rate.
Run →USB-C Display Path Readiness CheckCheck four documented prerequisites for sending video through USB-C, Thunderbolt, a dock, cable or adapter to a display.
Run →WebUSB Device TestRequest a compatible USB device through WebUSB and display the browser-exposed manufacturer, product, vendor, and product IDs.
Run →Decision table
What the observation changes
ObservationWhat it meansNext action
Peripheral works after moving to a different Type-C portPort capability/selection was the cause rather than a dead peripheral.Keep Thunderbolt devices on one of Dell's documented Thunderbolt 4 ports.
Basic USB works but Thunderbolt-only functions do notThe path may have fallen back to USB or be on the USB 3.2 Type-C port.Verify physical port and Thunderbolt-rated cable.
Device fails on both Thunderbolt ports and another hostPeripheral/cable becomes more likely.Test another known-good Thunderbolt cable or use vendor support.
Sequence
Work from reversible checks to escalation
- 01
Identify the two Thunderbolt ports from Dell's manual.
- 02
Connect the device directly to one of them.
- 03
Use a Thunderbolt-rated cable.
- 04
Compare the same device on another known-good Thunderbolt host if needed.
Likely areas
Keep these branches separate
Wrong Type-C portCable lacks Thunderbolt capabilityDock/peripheral modeHost firmware/driverPeripheral hardware
Repair boundary
When to stop changing settings
If multiple known-good Thunderbolt devices fail on both documented Thunderbolt ports, use Dell SupportAssist/pre-boot diagnostics and Dell support.