Having recommended DisplayLink (monitor connection over USB 2 or 3) to @jussipekonen I realised my own DisplayLink drivers needed updating: an update was made available on Feb 3. I bought my first Intel Mac in April 2007, so that means I've had the DisplayLink USB 2.0 to DVI adaptor since at least 2006 when I used it on a 14-in iBook. The DisplayLing jigger comes with DVI-to-VGA & DVI-to-HDMI adaptors.