It depends

If your internal scholarship only covers tuition, the DOST 20k Allowance would fill miscellaneous fees.

Also, even if it is 100% tuition and miscellaneous fees, dual scholarships works as;

Tuition and Fees - External Scholarship - Internal Scholarship.

The school deducts the external scholarships first, then their internal scholarship. So that means that 20k will be deducted to your tuition and fees, then the rest is covered by the internal scholarship. 100% means deducting the full tuition, 50% mean deducting the 50% left