Aside from the mysterious absence of a DVI port, the GTX 1080 Ti has a sophisticated cooling system needed to keep all of your games running smoothly in resolutions up to 4K.
The best entry-level GPU is the AMD Radeon RX 460. The RX 460 runs cheap. It is capable and energy efficient, drawing all of its power straight from the motherboard without any 6- or 8-pin connectors required. The RX 460 is worth the money if you plan on spending a lot of time playing MOBA and RTS games, otherwise spring for a higher end model.