Custom formatting looks different between Excel and the grid.
In excel it is the "$" symbol + right justified number. In the grid the "$" symbol is right next to the amount.
This may be an issue w/ the accounting format and not custom. See attached Screen shot.
1) open aspose_Grid_with_test_Fields_v10016.xlsx. (attached)
2) navigate to cell J26 for custom formatting added in Excel
3) navigate to cell L26 for the same custom formatting added in the grid.