Lonelec in UK has been, perhaps, the most reliable cable source over time. This link is for the set of two (including both the adapter cable and the FTDI chipped OBD->USB):
https://www.lonelec.co.uk/index.php?route=product/product&path=57_20&product_id=51
Regarding the comment on "smooth transition," this refers to checking resistance across the TPS while slowly opening and closing it. The values should transition smoothly with no jumps, skips, or opens (broken contact) that would indicate a faulty TPS.