The aim of this article is to help you better understand what power supply your computer may need depending on its most power-hungry component: the graphics card. The “Recommended PSU Wattage” value is for the whole system, not only for the graphics card/s.
I really wish articles like this didn't exist, given the number of really garbage power supplies out there. You get someone with a RX 480 and pair them up with some Chinese Firecracker 500w PSU which is only capable of around a combined 29A at 12v spread across two rails, like Rosewill Stallion Series RD500-2DB 500W ATX12V Power Supply-Newegg.com (12v1@15A, 12v2@16A), or APEVIA See-Through ATX-AS500W-BK 500W ATX12V Power Supply-Newegg.com (12v1@16A, 12v2@18A), or even the Thermaltake TR2 TR-500 500W ATX12V v2.3 SLI Ready CrossFire Ready Power Supply-Newegg.com (12v1@18A, 12v2@17A) and you're just asking for trouble, especially with units with gimmicks like transparent covers.
Yeah, but it's a good guideline. How many times have you had to look up power requirements for a certain graphics card? I am using it as a bookmark.
None, I use a SeaSonic X750
But it's easy. Set a base level of 300w for your CPU, motherboard, and all connected equipment not counting the graphics card, add 225w per graphics card (400w if dual 8 pin connectors), then add around 100w more for a capacitor degeneration buffer (~2% max power per year), and that should be your target, which comes out to about 750w for a single graphics card setup and 1100w in the case of a 4-way Crossfire setup with 4 8-pins.
I tell them 650-750w unless they have a lower end setup, like an APU, quality Corsair units of that size are around $60, plus it brings it in the 50% range for maximum efficiency, plus it also covers them if they do something stupid like buy some Chinese Firecracker.