Travellers routinely buy the wrong device for foreign power. Plug shape and supply voltage are separate problems, solved by different equipment, and most modern electronics only have one of them.
Two standards exist and both are common
Mains electricity worldwide runs at roughly two voltage levels, one around double the other, and at one of two frequencies.
Which applies is a matter of national infrastructure history rather than anything technical, and both are entrenched beyond any prospect of change.
Socket shapes proliferated separately, so there are many more plug types than voltage standards and no correlation between the two.
Countries sharing a voltage frequently use incompatible sockets, and countries sharing a socket sometimes run different voltages, which is why the two questions have to be answered separately.
An adapter only changes the shape
A travel adapter mechanically fits one plug type into another socket and passes the supply through unchanged.
It does not alter voltage, so plugging a single-voltage device into the wrong supply through an adapter delivers the wrong voltage directly to it.
Adapters also do not add an earth connection where the destination socket lacks one, which matters for appliances with metal casings.
Most electronics no longer need a converter
Laptop, phone and camera power supplies are almost universally designed to accept the full range of world voltages and both frequencies.
The specification is printed on the power supply itself, and a stated input range covering both standards means an adapter alone is sufficient.
Devices that state a single voltage require a converter or transformer, which is heavier and rated for a maximum wattage that must not be exceeded.
Heating appliances are the exception
Hair dryers, travel kettles, irons and styling tools draw high power and frequently carry single-voltage motors or elements.
Converters sized for these are bulky, and the wattage limits on small travel converters are usually well below what such appliances need.
Buying a dual-voltage version, or using what the accommodation provides, is generally simpler than carrying equipment to convert supply.
Practical points that get overlooked
A universal adapter with several sockets and integrated charging ports reduces both bulk and competition for a single outlet.
Older buildings often have few sockets and none near the bed, so a short extension lead is more useful than an additional adapter.
Devices with motors or clocks can behave differently on the other frequency even at the correct voltage, which affects appliances more than chargers.