Pulse Width Modulation (PWM) is a modulation of the duty cycle. The duty cycle reflects the switch between two fixed values, such as 0V and 5V. The frequency of the signal never changes in the process. The only factor that varies is the rhythm of "on time" and "off time". For example: a 50% PMW would set a fan – such a CPU or casing fan – running at approximately half of its maximum RPM.
A power supply delivers the necessary current to devices operated on the European 230V domestic network (or 110V in the USA and Japan). The power supply works here as a voltage convertor, converting the 230V alternating current into specific direct currents.
Active PFC stands for active Power Factor Correction. This is a filter to minimise disruptive harmonics. The highest possible value for an active PFC is 1.
PF stands for Power Factor and in electronics refers to the ratio between real performance and apparent power. The power factor can be no more than 1. The closer to 1 the PF comes, the better that loss is avoided during transmission.