Converters are not usually sold as adapters for a good reason. The majority of the converters around the world receive 220-240 V single phase at 50-60 Hz.
While most of the countries have a single defined plug type, a lot of countries in Latin America, Africa, and Asia have a collection of incompatible plugs for different wall outlets. Although there is standardization among the states regarding the voltage used in domestic appliances, there is still a difference between the 220-240 V standard and the 100-127 V standards.
Typical Residential Power
The mains power is the general-purpose AC electric power supply that is used in homes and businesses. It is usually used for domestic appliances. The mains power is different in voltage and frequency. Of course, trying to use an incompatible value can destroy the Ammeter Shunts in your devices.
Generally, the power is delivered in a household using two or three wired contacts. The first is the line wire. This hot contact carries the AC between the power grid and the home. Next is the natural wire, which completes the circuit and gives the AC. Lastly is the ground wire, which connects the equipment to the earth ground to protect against any electric shocks.
The measurement on the single hot wire in connection to neutral or ground is the value for the voltage. This value generally drops when it reaches an appliance, given the resistance in household wiring and the distance of extension cords. It is one of the primary reasons behind values other than the mains voltage that is used for appliance ratings.
Origin of Voltage Standards
Thomas Edison, in 1882, started the first large-scale central electric power plant. It provided a direct current (DC) at 110 V for 968 light bulbs in London. This voltage was regarded as a safe voltage for consumers to use. It was also the ideal voltage for the filaments in his lightbulbs.
After the London plant, the AC systems slowly emerged in the United States. They used transformers to step down higher voltages from distribution. Edison then patented a three-wire distribution system in 1883 to provide versatility for many users. It gave way to the War of Currents.
Depending on the ground connection, the wetness or resistance of their skin, and duration, these factors play a role in determining the real safety concerns for a person dealing with electrocution. However, in modern times, circuit breakers, GFCI outlets, and AFCI outlets have helped a lot in addressing the electrocution and fire concerns of mains power.
This is the kind of system we have today. There aren't any significant plans to unify standard mains internationally. It can be prohibitively expensive to convert from one system to another. The manufacturers of electronic devices have for made this a non-issue by designing power supplies that will function on 240 V, or 110 V. Consumers will only need a simple converter to make the vast array of outlet types work correctly.