there is a WAKE# pin on the PCIe slot so any card should be able to wake the system from sleep (S3). however, an ATX PSU supplies only 5V (5Vsb) when the syste

there is a WAKE# pin on the PCIe slot so any card should be able to wake the system from sleep (S3). however, an ATX PSU supplies only 5V (5Vsb) when the system is off (S5) which is not available on the PCIe connector which only has 12V and 3.3V. so when the system is off (S5), the PCIe cards are unpowered and thus cannot turn the system on. but if you mean off in the Microsoft "Modern Standby" (S0i) then yes, the PCIe cards are powered and the WAKE# pin can "turn on" the system.