There are a lot of cruddy video card cables out there. Fortunately the LG 27UL500-W panel is quick to discover them. The panel has 2 HDMI inputs and one DisplayPort input.
HDMI cables are limited more by the shortcomings of the standard than anything. HDMI at 1920×1080 is designed for longer cables for display purposes such as the setup at many mall restaurants.
USB panels are a newer product in the market. USB-C has enough bandwidth and power to handle fairly long cables.
DisplayPort is royalty free. It is also designed for much more bandwidth than HDMI. Cable lengths are shorter due to the higher frequency signals.
Good quality cables can be more expensive. There are also some overpriced garbage cables out there.
The GTX 690 has dual link DVI outputs so I use a DVI to HDMI cable rather than a conversion dongle. The GTX 690 works fine on the LG panel at 3840×2160. Conversion cables are common and they are far easier to take advantage of compared to dongles which often are hard to keep in place etc.
DVI to VGA cables are also available which are fine for a legacy display. Some use an old LCD or even a CRT as the cost of the LG 27UL500-W is more than many can afford.