I just wanted to post this info in case anyone might face a similar issue. I have several Dell Optiplex 7010 workstations that I wanted to use for gaming machines on my LAN. The problem was they all had 275 watt power supplies, and no PCI-express power connectors. This posed a problem since the XFX RX460 4GB cards I purchased from Best Buy required the 6 pin PCI-express power. I found this connector on Monoprice.com and bought 4 of them 8inch SATA 15pin to 6pin PCI Express Card Power Cable - Monoprice.com
I had to disconnect the front panel USB header where it plugged into the motherboard because the video card shroud hit it. Other than that I was good to go. I tested with my Kill-a-Watt power meter and it only hit 161 watts while playing Heroes of the Storm on high settings at 1080. This is with a Core i5 2400 and 8 GB of system ram. I made a short video for reference Dell Optiplex 7010 with XFX Radeon RX 460 4GB - stock power supply - YouTube
My point with all this is that you could probably do something similar with a computer that had a similar power supply. Please note however, that even though it is only rated at 275 watts, the power supplies that Dell uses should be considered fairly robust since the Optiplex is a workstation and not simply a home computer.
I hope this helps someone, and maybe saves you some money buying a power supply that you don't need.