They are designed to operate of 230 V AC. They rectify this to DC and a simple rectifier will convert 230VAC to about 340VDC. When operated in 115V mode, they use a voltage doubling circuit to generate the 340VDC.
PSUs with active PFC achieve PFC by using a step-up DC-DC converter to produce about 380-400V. A voltage doubling circuit is not required in this case, the step-up converter will automatically produce the high voltage as long as the incoming DC is above about 100V.
The high-voltage DC is then passed through a step-down DC-DC converter to produce 12V and 5V.