Mac Mini 2018 VGA Adaptor

I have a Mac Mini 2018. I purchased a Usb-C to VGA adaptor. When I plug everything in and turn it on, the monitor stays black. It seems as if the mac doesn't recognize that a display is attached.

However... if I plug in a HDMI monitor (directly to the HDMI port on the mac) and the same UsbC/VGA adaptor together, they both work fine as expected.

Further, if I unplug that HDMI monitor, the VGA one continues to operate fine until the mac is rebooted.

Shouldn't the mac work with the UsbC/VGA adaptor as the only display ? I'm wondering did I get a wonky adaptor and should I exchange it.

Anyone else have these issues?

Thanks