quad cores dont excist really m8, u mean intles 2x2 then yeah but still they arent very power hungery really, and the 6800/7800 where the best cards from nvidia at the time he wrote this.
really any psu from the top companys will power an x1900 card without worrie,people worrie to much about rated wattege insted of build quility and true ampage.
my 2 305watt 15amp 12v rail enermax(like 4-5 years old if not more) can both power this whole system even under full gaming without faultering, where i have seen 650-750 watt psu's fail to work with a 9800se becuse the card drew to much power!!!!!
any fortron400+ watt dual rail unit(like mine) or epower dual rail 400+watt unit will power a heavly loaded system without a problem, my psu dosnt even get warm(its not struggling) after 6-8hrs strate of gaming, yet its BELOW the "requiered wattage" specs given for an x1900xt(check how much stuff i got in this system)
please remmber that this guide is over a year old, he hasnt updated it because it was in the chaintech forums and chaintech stoped making motherboards.
but the info as i said is still good, it gives you what you need to know to choose a decent psu without paying an arm+legg+left nut+first born child