I'm not an electrician or electrical engineer, I'll do my best to explain my understanding. There are 3 kinds of differences: different sockets, different voltages, and different frequencies. Basically, there are 4 options for dealing with the different electrical systems around the world:

1. Buy new stuff
2. Buy an adapter, it allows you to connect a device into a different kind of socket but it doesn't change the voltage or frequency.
3. Buy a converter or transformer, it allows you to connect a device into a different kind of socket and it adjusts the voltage but it doesn't change frequency.
4. Buy a voltage regulator, it takes care of everything.

Lots of companies market adapters and transformers to travelers, but they rarely explain that transformers do nothing about frequency. This can cause problems with any class of device but its especially bad for motorized items because the motors are designed to operate at a specific frequency and giving them electricity at a different frequency forces them to operate in a way they were not designed, this tends to wear them out more quickly. Another big issue with transformers is they don't do anything to protect against brownouts or power spikes, which means you risk damaging sensitive electronics.

There are all kinds of voltage regulators, they tend to do the best job but they are heavy becuase they include motors or other components that are bulky.