If you are going to use electrical appliances in another country, you need to know what type of electrical voltage is used in the country you're traveling to and the type(s) of plugs and outlets used there. To learn this, consult the Table of Electrical Systems used worldwide.
If the voltage is the same, or if you're using a universal power supply (see below), all you may need is a plug adaptor. Converters are available to change line voltage from one amount to another. However, there are different types of converters for different types of appliances. Small electronics, razors and non-heating appliances can operate with a 50-watt converter. Heating appliances such as hair dryers, irons, coffee makers and other high-power electrical appliances need a 1600-watt converter. You can also purchase combination converters for both types. Check the label on your electrical appliance to find its wattage. Some places that supply adaptors and converters are listed on the sources page. These generally work for those from the US traveling to destinations that use higher voltages to "step down" from 230V to 120V.
On the other hand, those who travel from a good portion of the world to the US will likely need a transformer to convert the lower line voltage into the higher voltage required by their appliances. Many of these devices (sometimes of higher quality and thus higher-priced) also function as step-down converters.
Also, since the quality of electrical power might be an issue, a Universal Surge Suppressor might be a goody buy, especially one that includes plug adaptors that will work in most of the world.
In addition to voltage, the frequency at which the power is generated may also differ, usually from 50 Hz to 60 Hz. Does this matter? Yes, it might. Click this link to read more on this issue. While it is possible to convert voltage, it is not possible to convert frequency, though some devices are built to handle these differences as discussed below.
Given the complexities of safely using your electrical appliances overseas, you may want to consider some alternatives. If you plan on staying in one country for awhile, you might want to buy a hair dryer or electric razor there. Battery operated appliances are another option if you don't mind replacing the batteries.
If you are interested in converting electrical units or sizing a generator try these Power Generator Calculators (for calculating generator size in kW, converting kW to kVA, kVA to kW, Volts, Amps, and more).
WHAT ABOUT YOUR COMPUTER, camcorder, CD/DVD player, etc?

Fortunately, many portable computers today come with power supplies that can be used in almost any part of the world. Check the manufacturer's label to see what type of input it can handle. This applies to many digital cameras, VCRs, video games and other electronic devices as well.
Those designed for use just about anywhere have a section on the label that looks something like this:

INPUT: AC 100V- 240V~ 1.0A 50 / 60 Hz

This shows that the device was designed to be used over a wide range of voltage levels and at different electrical frequencies. In this particular example, the device can accept “nominal” voltage anywhere from 100 volts to 240 volts and can operate on either a 50 Hz or 60 Hz system. It is designed for alternating current (AC). (Like most appliances, it should not be used on a direct current, or DC system -- DC electrical systems are not common, but some may still exist.) If your device has a label with these parameters, it can be used pretty much anywhere. In that case, all you need is a <A href=" tor_KitsEA240K?Partner_ID=CJLNK&cjsku=EA240K" target="_top"" target=_blank>plug adaptor.
If you must take other types of electrical appliances with you abroad, your best bet is to buy travel-size dual-voltage appliances that can run on both 110 and 220-volt currents. Make sure the switch is on the proper voltage for the country you are in before using the appliance. You will also need to carry adaptor plugs with you to fit the outlets in the countries you're visiting.

The main types of electrical plugs that are used around the world are listed below. You can click on the illustration to view a larger picture and a listing of countries where that type of plug is used. Note: the illustrations below are not to scale. Also, the labels (type A, B, etc.) used by my principal source listed below are not any type of standard nomenclature; labels and descriptions used by <A href="">various vendors may differ. Supposedly the <A href="">IEEE has standard terminology for these things, but it's not used by anyone in the travel industry.