A quick search turns up the following categories:
Actual TSP (trisodium phosphate)
TSP-PF (phosphate free) - what's the significance?
TSP "substitute" - still not clear what this actually means
"Trisodium Phosphate removes greasy, sooty dirt and prepares surface for repainting" is a typical description.
What are the practical differences among these alternatives? I assume they can't all function identically.