Source Depot was based on Perforce. Microsoft bought a license for the Perforce source code and made changes to work at Microsoft scale (Windows, Office).
TFS was developed in the Studio team. It was designed to work on Microsoft scale and some teams moved over to it (SQL server). It was also available as a fairly decent product (leagues better than SourceSafe).
Source Depot was based on Perforce. Microsoft bought a license for the Perforce source code and made changes to work at Microsoft scale (Windows, Office).
TFS was developed in the Studio team. It was designed to work on Microsoft scale and some teams moved over to it (SQL server). It was also available as a fairly decent product (leagues better than SourceSafe).
None that I know of, Source Depot is derived from Perforce.