This is a transformer casing to fit inside a 2011 Nissan Leaf EVSE.
If you buy a second hand Leaf from Japan it will probably come with an original Nissan LEAF EVSE - rated for an input voltage of 200VAC.
This is a problem if you live in a country with 240 VAC mains. The transformer that supplies power to the control chips inside the EVSE charge cable box will be running 20% above it's nominal rating. After a few months of overcooking it'll die.
To avoid (or repair) this problem you can replace the transformer with one rated for 230VAC from RS Components: RS PRO 6VA 2 Output Chassis Mounting Transformer, 18V ac (https://nz.rs-online.com/web/p/chassis-mounting-transformers/0504757/). This unit outputs 18VAC instead of 19VAC that the original unit output, however it works fine.
The transformer casing provided here fits the RS unit perfectly and is a drop-in replacement (but tight) for the original one.
Note: this only works for the 2011 EVSE. In later models the transformer is potted into the unit and would be quite hard to extract. And I don't know if this RS transformer will fit the later EVSE models.