Power Consumption: Idle
Desktop Mode Without Load
As with the Radeon HD 7990, AMD's Radeon R9 295X2 features AMD’s ZeroCore Power capability, which is active in two different states. It's important to make a distinction between a powered-on display with Windows idle and a powered-down monitor triggered by Windows' profiles.
When ZeroCore Power does its job, consumption drops from 28.5 to 13.5 W at idle, as one Hawaii processor is turned off. Then, the display switches off as well, and power use drops to 6-7 W. At that point, even the card's fan stops spinning.
In case you're missing the 3.3 V rail's blue line (as we were at first), all of the Radeon R9 295X2's components pull from the +12 V rail now.
Comparing To The Radeon HD 6990 and 7990
If you take a close look at the chart below, you'll see that the +3.3 V rail was used by the Radeon HD 7990, if only just barely. Also, nearly all of the power is provided by the card's auxiliary connectors, rather than the motherboard's slot.
The Radeon R9 2905X2's behavior is more similar to cards like the GeForce GTX 780 and 780 Ti, while AMD's older models are mainly driven by the separate power leads.