How do I upgrade my GX280 so it can play smooth 1080p video smoothly when displaying full screen? I have a Dell Optiplex GX280.
Keeping in mind that it only has a 250 wall PSU.
Basically for this kind of power supply and low profile PC (assuming it is NOT a shopping question, but asking how you can play back fullHD content on a low-profile, not-so-strong PC), you need a GeForce card. NVidia Geforce. Why? Because it comes with VDPAU.
You can play all the HD content on Linux if the card comes with VDPAU.
'Smooth' 1080p playback isn't so much a function of the video card as a function of how fast the computer can decode the video and create a framebuffer for display to the video device. More powerful GPUs increase the speed of 3D gaming more than 2D video playback. A fast, expensive GPU on a slow computer will still render the video slowly.
If you want it for gaming, then the more graphics memory for texture caches the better.