PhD Scholarship Top-up If I receive a large scholarship (i.e. greater than $20,000), should my supervisor top up the award? If so, do I simply ask my supervisor, or is a top-up seen as a "gift"?
This really depends on the graduate department. 

At a minimum, however, you should not expect to come up "short" on funding because you brought in an external fellowship. Someone should offer up additional money to bring your total package up to the standard level given to your colleagues in your department. Whether or not the funds come from your supervisor or from the department is for them to decide.

The exact mechanism also varies by department. For instance, in the departments I applied to as a graduate student, one gave a sizable bonus for bringing in an external fellowship (an extra $8,000 per year), while others "topped off" the stipend up to 110% of the stipend of students' normal stipend.