The first thing you should know is that your power supply must be compatible with the AC voltage used in your city. The most common ones are “110 V”, which covers voltages around this value like 115 V and 127 V, and “220 V”, which covers voltages around this value like 230 V and 240 V.

Most power supplies will have either a 110 V/220 V switch or will be “auto range” or “auto select”, meaning that they can work under “any” AC voltage (usually between 100 V and 240 V; the range is printed on the power supply label, under “AC Input”, see Figure 3) and thus not bringing this kind of switch. Usually manufacturers make the “auto select” circuit thru the active PFC circuitry. So all power supplies with active PFC will be “auto range” and won’t have a 110 V/220 V switch. Only a very few power supplies with automatic voltage selection won’t have an active PFC feature. Of course we will explain what this circuit is later.

Also not all power supplies that don’t have a 110 V/220 V switch are auto range. Some power supplies can only operate under a specific voltage and this case is most common on some power supplies targeted to the European market. So if you see a power supply without a 110 V/ 220 V it is always good to double check on the power supply label the AC voltage it can work under.

click to enlarge
Figure 1: Power supply 110 V/220 V switch.

click to enlarge
Figure 2: Power supply with auto voltage select – no 110 V / 220 V switch. Usually this means that the unit has active PFC.

click to enlarge
Figure 3: The voltage range for power supplies with auto voltage select is described on the power supply label.

The connection between your power supply and the AC outlet is done thru a power cord. This power cord must use a plug compatible with the standard used in your country or you will need to use an adaptor. The two most common plug types are the North-American (NEMA 5-15) and the European (CEE 7/7). Other countries may use different plug types (for example, the UK use a plug called BS 1363).

click to enlarge
Figure 4: North-American power cord.

click to enlarge
Figure 5: European power cord.

The end of the power cord that is connected to the power supply uses a trapezoid-shaped plug called IEC C13, while the receptacle for the power cord located on the power supply uses a plug called IEC C14. Other plugs can also be used on this connection, like IEC C19 and IEC C20, but they are not so common.