I bought a Displayport to VGA adapter.
Its for connecting my 3th screen since i have no other connections that are free.
I have a GTX660 DC2O 2GB. (1xHDMI 1xDVI-D 1xDVI-I 1xDisplayport)
And 3 ACER AL2216W monitors, and 1 of them has DVI besides VGA.
According to the web and shops, the adapter supports 1920x1080.
However i only need it to be 1680x1050.
I connected it but it only shows 1280x1024 as max native resolution.
The screen also isnt detected by windows correctly.
I deinstalled the monitor and added it manually. It now says i have a ACER 2216W, wich is correct.
But still only 1280x1024.
If i connect my laptop to it on VGA, the resolution can be set to 1680x1050, So its something with the displayport... However, according to all info, displayport>VGA-adapters should have support till much higher resolutions...
It sounds like you have a bad adapter. I ran into similiar issues in the past. The best adapters to get are the Displayport to DVI adapters, then from there use a DVI to VGA dongle (should have gotten one with your video card). When my original adapter died it showed the same symptoms, it showed the monitor and let me activate, but I was limited to an extremely low resolution. When I got my second adapter, I would occasionally get an error saying "Displayport link failure" after the computer woke from sleep and the monitors resolution would be off. A reboot would usually fix it in that situation. Eventually I upgraded to 3 monitors with displayport and I still occasionally get the displayport failure mesage and have to reboot, but its not that common.