For information on individual plug types please refer to Domestic AC power plugs and sockets. For information on exactly where plug types are used, please refer to the List of countries with mains power plugs, voltages and frequencies.
These do not convert electricity. They simply allow an appliance (dual-voltage if necessary), a transformer, or a converter from one country to be plugged into the wall outlet of another country. Adapters sometimes do not make an earth connection, and so may be unsafe. For UK and Hong Kong natives and visitors, you can visit page Common electrical adapters in Hong Kong and the United Kingdom for adapters available for you.
These can be made up from appropriate plugs and extension sockets (or power strips if more than one socket is required) and cable. This method has the advantage of allowing use of the exact right parts (adapters often attempt to generalise which can lead to loose fitment and easy disloging). Another possibility is to make an adaptor lead with an IEC male plug (with pins as on the cables used to connect power from older PC PSUs to monitors) and an appropriate power strip. This can then be connected to a local power cord which should be easily obtainable in most countries. If not there is still the option of unscrewing the IEC male plug and screwing on a locally purchased plug.
Transformers are used with "electronic" products. Electronic products have a chip or transistorized circuits. Examples are radios, CD or cassette players, shavers, camcorder battery rechargers, computers, computer printers, fax machines, televisions, and answering machines. Transformers can also be used with electric appliances and may be operated continuously for many days.
Different transformers are available for appliances of different power ratings. Most products have the power printed somewhere on them, although some products list only amps. A rough conversion for the USA and other 110 V countries is 1 amp equals 100 watts, and for European and other 230 V countries 1 amp equals 200 watts. The power of the appliance must fall within the range of the converter or transformer being used (allow a margin of at least 10 watts).
Computers are electronic devices and therefore they must be used with a real transformer. It appears that there may be other conversion methods around which may damage electronic equipment. Some PC power supplies have a voltage switch, on the back of the case, for 110 V or 220 V — this should never be set incorrectly, and should always be checked if a PC has come from an unknown source or may have been tampered with. Laptop battery chargers, and AC adapters generally have a universal input which can take a wide range of voltages without manual switching. In general, if an appliance has an input that can accept the local voltage, it is generally better to connect it directly (using a plug adapter or adapter lead if needed) than to use transformers or other forms of voltage conversion.
Anyone who travels much is sooner or later likely to find themselves in a situation where no earth is available or the earth that is available won't join with any of their plugs or adaptors. Also, just because sockets have earth contacts doesn't necessarily mean they are actually connected to a properly designed and safe earthing system.
For this reason wherever possible double insulated equipment is the smart choice for the traveller. Where single insulated equipment is all that is available and the sockets have no earths or dubious earths it is best to at least ensure that the earths of all appliances likely to be touched at the same time are connected together (for example by plugging them into the same powerstrip with earth contacts). This way if one of the cases becomes live they all do and therefore there is minimal voltage between them and therefore touching them at the same time won't give a shock (remember current has to flow between two points on a persons body to give a shock). The worst thing to do in this situation is join the earths in groups which are isolated from each other (for example two powerstrips with earth contacts in two unearthed sockets) as this will spread a fault without providing an equipotential zone throughout the equipment.
Radio and television receivers use different bands of frequencies in different parts of the world. For example a North American NTSC receiver will not operate in countries using the PAL television standard or on the different channel assignments for Japanese NTSC television. AM (medium-wave) broadcast stations are on 10 kHz frequency spacing in North America and 9 kHZ in other parts of the world; some digital tuners may have a switch to allow for different spacing of the assigned frequencies.
Operation of receivers may require a licence or permit or tax to be paid, even if the receiver is technically capable of operating with local standards. Some governments restrict traveller's use of GPS satellite receivers.
Personal radio transmitter devices, such as amateur radio equipment, FRS, GMRS, MURS, or Citizen's band transmitters may not be permitted in different countries. Frequency assignments dedicated to these services vary by country and an FRS transmitter may interfere with local public safety or business communications.
Power frequency is 50 Hz in much of the world and 60 Hz in North America and certain other regions. Some motor-operated devices may work at different speeds even if a transformer is used to change the voltage. For example, very old tape players and record players may not work properly as the pitch of reproduced sound will be off. As a rule of thumb, if the equipment also operates on internal batteries, it will not be sensitive to power system frequency.