AMD recommend a 750W power supply with 42A on the 12V rail at least to run their HD6990 and after seeing the load power draw, it is advisable to listen to AMD. At the default speed, the power draw matches a GTX480 and is only 20W higher than an overclocked HD6970. This is very impressive from a performance per watt perspective. AUSUM mode increases the power draw significantly due to higher clocks, voltage and increased PowerTune TDP. It ends up less efficient than an overclocked GTX590. Overclocking the HD6990 only increases power consumption further, but not on the same extent as before implying that the card’s TDP was being met and consequently the card was throttled.
