wow! the gpu name is confusing - I though it's a typo
so after realizing it's not a typo here goes my pre-serach about this
here it says uit needs a single 6 pci-e pin power adapter :
Radeon HD 6790 to released on April 5th- Techpreview.in!!! - Lastest Technology News
but this says it needs double - confusing
Exclusive: Radeon HD 6790 based on Barts LE with 800 SPs - www.nordichardware.com
^^ stay tuned - those guys ^^ above said they will get exact info about power consumption by the last date of this time anyway.
It's not all rosy however, as the HD 6790 suffers from one of the same crippling flaws of the HD 5830 - high power consumption for the performance. As the HD 6790 is built around salvage dies, it requires a higher voltage than the regular Barts products to keep its clock speeds high sufficiently. The result is a 150W power consumption and requirement for 2x6-pin
UPDATED: AMD Radeon HD 6790 Specifications Revealed - VR-Zone.com
meanwhile - while we wondering about power consumption let us enjoy some cool pics and say some WoW !
*www.fudzilla.com/images/stories/2011/March/General_News/sapphire_HD6790_3.jpg
pic courtesy of fudzilla.com
Sapphire's HD 6790 pixellized