laptop - External monitor turns off after 15 minutes - when machine is being used

One of the users in my company has a Dell XPS13 laptop, with an external monitor connected via a USB > VGA cable. After around 15 minutes of the laptop being used, the video on the external screen cuts out and the monitor goes into standby. The screen on the laptop stays on. The power setting is to "do nothing when lid is closed" so the second screen stays on when the laptop lid is closed.

The issue can be resoved by unplugging the USB > VGA converter but this is not a desired behaviour of a £1000 machine.

I have:

• Swapped the screen out with a spare


• Updated the graphics drivers for the USB video adaptor and the Intel Graphics Driver


• Swapped the VGA cable


• Tried using the Mini Displayport to output to the screen (Mini Displayport > DVI cable) - screen does not turn on at all.