LookupEdit is an editor that retrieves elements for its DropdownWindow from the underlying DataSource. That is, he demanded that the ValueMember, DisplayMember, and DataSource properties be set.
ComboBoxEdit gets items from its Items collection.
The standard WinForms comboBox is a mixture of these two editors and can work in both modes.
In addition, here is a useful article:
Can I bind XtraEditor ComboBox to datatable?