Hi grumpysmurf,
I would suggest you to update the BIOS and reinstall the chipset driver on the system for issue resolution. Please enter your service tag # on the link below, select the OS, then download the BIOS from BIOS section and Chipset driver from chipset section onto the system and install it.
Also, please follow the steps below to run the diagnostics for the USB ports on the system.
1. Open the link http://dell.to/11MXNII
2. Select ‘Hardware’ under ‘Dell PC Diagnostics’.
3. Select ‘USB’ under ‘Diagnostic Selector.
4. Click on ‘Run Diagnostics’ button.
5. Let me know the results.
Please let me know if this helps.