Transformers (Transformer) to transform 220 V - 230 V - 240 V to 110 V - 120 V. E.g. to run european devices in US or in other countries with ca. 120 V.
Transformers (Transformer) to transform 110 V - 120 V to 220 V - 230 V - 240 V. E.g. to run US-devices (110 V ~ 120 V) in Europe (230 V ~ 240 V) or in other countries with ca. 230 V.