The leaked photo shows the RX580 will feature a 6-pin and 8-pin PCIE power connectors. Despite the additional power connector, the VRM appears to be a 6-phase design, which is the same as the reference RX 480.
While the source link is no longer available, it would seem that someone has gotten their hands on a (golden) sample, one of the two different SKUs that PowerColor is expected to launch around the RX 580. This Golden Sample edition sports a beefier, higher-performing 2.5-slot cooling solution, compared to the expected RX 580 Red Devil’s 2.0-slot one. This sample, however, sports something unusual for a card with the power envelope expected from the RX 580: two auxiliary power cables, one 6-pin, as is par of the course with previous-generation RX 480 cards of which the RX 580 is a rebrand; and another, 8-pin one.