By default, an ArcadeVGA only outputs CGA signals (~15.7 KHz Hsync rate), so a computer monitor won't work straight away (30+ KHz Hsync signal required).
The card is designed to be plugged on a SCART TV, an arcade monitor, or some other kind of RGB monitor compatible with CGA resolution 0.7 Vpp video.
The AVGA's "Trisync" patch frees up VGA+ modes so you can use a 30+ KHz non-interlaced display. It is also said that once you have enabled this, if you reinstall the AVGA driver you will be back to your previous state (all modes timed at ~15.7 KHz), but the thing will resort to 31+ KHz Hsync modes for VGA+ if connected to a DDC enabled suitable display (a PC monitor).
With this trick you can still use your CGA display with full safety, and be able to show the windows desktop on a PC monitor.
Cheers