The cable works fine, as long as the 4K monitor (Asus PQ321) was configured as a single monitor at 30Hz, except that, of course, this setting can not be satisfactory. When I tried, by switching to MST (Multi-Stream) and set up a 2-monitor group to get horizontal in AMD Eyefinity a 60Hz display, I announced the AMD Catalayst Control Center a 'Link error' and said that it could are on cable.
I took off the cable and lock instead the DisplayPort cable that came with the 4K monitor. And now the problem was gone.
Conclusion: The cable, run clean and quality is obviously limited in its power, just that so far this limit never played a role. Now that 4K monitors are there and want to operate at 60Hz, the cable does not deliver the required power (presumably. Due to lack of data lines).
I have Amazon informed, returned the cable, and now looking for a cable that declares itself as "responsible" for this high data volume. This is not easy at the moment.
