I have an Optiplex 745, "desktop" chassis (smaller than the mini-tower, bigger than the small form factor). It has 1 PCI Express x16 slot. I've tried the VisionTek Radeon 1GB 6570 DMS59, mDP B2 PCIe card, but now Dell tells me it only supports two monitors at a time. I also tried a VisionTek Radeon 5450 PCIe 512M SFF Dual DVI B2, which has two DVI ports and a mini-DP, but it takes up two slots and the way the slots are positioned, it won't physically plug into the motherboard, so that's out.
I'm wondering if anyone knows of a PCI express x16 card that takes up one slot and will support 3 monitors.
Or alternatively, if I can use the 6570 for two monitors and add a USB-VGA adapter for a third monitor. No gaming on this machine, just big spreadsheets.