It starts off by examining how much wattage your system actually needs. Then they talk about efficiency and noise. They even provide 3 systems as examples to demonstrate power usage and efficiency. Then they discuss the most important issue, the 12volt rail..
The power supply is the heart of your system. There is a quality, feature set, performance and efficiency line that gets crossed with power supplies greater than 600 watts. While you can run an 8800 ultra with a 400watt power supply, 400 watt ps's don 't have the connectors required to power the card.
At the beginning of the year, we requested a special AnandTech Edition of PC Power & Cooling's Turbo Cool 860W power supply with six PEG connectors, specifically for running a triple-SLI setup. We have been using the power supply since then with three GeForce 8800 Ultra cards, an Intel Core 2 Extreme QX6850 CPU, and 12 Western Digital hard drives without any problems. Clearly, quality of construction and number of connectors are far more important than a silly wattage rating.
We generally recommend at least a 600watt ps for most gaming systems. We do this because we know that the quality, efficiency, features, and wattage requirements are going to be met. It also gives you some room to upgrade, should you want to do so in the future.