New answers tagged displayport
There is nothing wrong with your monitors, neither your Mac. That's a compatibility issue with your adapter. There are many comments on Amazon complaining about the same issue on similar converters. That seems, unfortunately, a hardware fault. Example: http://www.amazon.com/gp/aw/cr/B00NH13I08/ref=mw_dp_cr
Since Retina is an Apple trademark, the "official" answer is no third-party display gets that recognition. According to wikipedia, all Mac that are marketed with Retina displays have a pixel density of 220 PPI or thereabouts, so you could make an argument that any external display that's IPS and at least 220 pixels per inch would be in the "Retina class". ...
Here's one that'll really cook your noodle: Yes, the hardware in a MBP will support this (I've done it on MacBook Pro 15", mid 2014). But no, it only works if you're using Bootcamp and booted into Windows. Apple has chosen not to support this in their drivers and software.
Thunderbolt and DisplayPort are not compatible. They only share one port. Thunderbolt uses active transmission (there's a chip in the cable), DisplayPort uses a simple copper cable. You should be fine with using a DisplayPort cable.
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