Power Factor CorrectionWarning: Spoiler! (Click to show)
Power Factor Correction (PFC)
Power Factor Correction (PFC) allows power distribution to operate at its maximum efficiency.
There are two types of PFC, Active PFC and Passive PFC. All of our power supplies are either Active PFC Power Supplies or Passive PFC Power Supplies.
Most quality power supplies include Active PFC. Currently only lower quality power supplies use Passive PFC. Most people prefer to use Active PFC power supplies since Active PFC is more efficient and does not require manual switching when switching between different voltage (depending on which part of the world you are).
Inside A Power Supply
The preferable type of PFC is Active Power Factor Correction (Active PFC) since it provides more efficient power frequency. Because Active PFC uses a circuit to correct power factor, Active PFC is able to generate a theoretical power factor of over 95%. Active Power Factor Correction also markedly diminishes total harmonics, automatically corrects for AC input voltage, and is capable of a full range of input voltage. Since Active PFC is the more complex method of Power Factor Correction, it is more expensive to produce an Active PFC power supply.
Passive PFC uses a capacitive filter at the AC input to correct poor power factor. Passive PFC may be affected when environmental vibration occurs. Passive PFC requires that the AC input voltage be set manually. Passive PFC also does not use the full energy potential of the AC line.
Non-PFC power supplies are no longer recommended. In Europe, power supplies are now required to have either active PFC or passive PFC.
Alternating current outputs sine wave and direct current is pure.
Since UPS has a battery, DC voltage has to be inverted to AC voltage, thus creating artificial sine wave (in cheap UPS's). That's why they created UPS with "pure sine wave" output as if the UPS acts like true a AC wall outlet.
Addressing to the Active PFC and "Pure sine wave" UPS question, here's the answer from Cyberpower.
"Your computer uses a power supply that utilizes Active Power Factor Correction (Active PFC) to improve efficiency. Power supplies with active PFC may experience incompatibility problems with a UPS that does not provide pure sine wave power output when the power supply switches from AC power to UPS battery power. As a result, when a computer system using a power supply with active PFC is attached to a non-sine wave UPS, the system may shut down when it switches to battery power. Also, if the power supply continues to operate, it may produce a humming or high pitch noise while running on battery. This humming indicates the power supply is operating beyond specified tolerances and may damage the power supply.