You Do Need power plug adapter while traveling from East Timor (Timor-Leste) to Mongolia.

Here is Why You Need An Adapter

The outlet and plug type used in Mongolia are C and E and in East Timor (Timor-Leste) are C, E, F and I. This is how they look like.

East Timor (Timor-Leste)

In East Timor (Timor-Leste), outlets of type C, E, F and I are in use.

Type C

Type E

Type F

Type I

Mongolia

In Mongolia, outlets of type C and E are in use.

Type C

Type E