Doesn't fit the native resolution in Samsung S22D300 monitor on Radeon R9 280

The VGA connector is analog. They date back from the CRT days when monitors didn't have a fixed resolution, just different horizontal and vertical scan rates they were capable of. So a VGA connection doesn't tell your video card the max resolution the monitor is capable of, just the max horizontal and vertical scan rate. This is done through two pins which control the v-sync and h-sync.

It sounds like one or both of your pins aren't transmitting this info properly. The fault could be in the monitor's VGA port, the VGA cable, the DVI to VGA adapter, or your video card's DVI port. When the video card doesn't know the max v-sync and h-sync frequencies the monitor is capable of, it errs on the side of safety and chooses the minimum - 1024x768 in your case. The reason is because trying to drive the monitor at a higher frequency than it's capable of can destroy the monitor. This is one of the few parts of a computer where a software setting can damage or destroy hardware.

Doing what rhysiam suggested is probably the best solution. Straight HDMI or DVI to HDMI will give you a pure digital signal so no more sync issues, and the picture might even become slightly clearer. The only catches are some monitors reduce your color tweaking options with a digital signal (the option is there because of possible color signal degradation in an analog VGA cable). And some monitors will assume HDMI is a video signal and automatically overscan it (make the picture larger than the screen, cutting off the edges), meaning you'll have to figure out some way to turn overscan off.

If you insist on using the VGA connection, you have two options. You can go through all the parts I listed and replace them one at a time to figure out what's causing the problem (my bet is the DVI to VGA adapter). Or you can see if there are monitor drivers for your Samsung S22D300 monitor. Monitor "drivers" aren't really drivers, they're just a list of supported resolutions and sync frequencies. Windows uses that info to determine what resolutions and sync frequencies to show you as available.