The pci-e slot provides enough power for the graphics card. I've used some combination of three cards in two different mini-itx motherboards and have not had any problems. Well, at least not with Windows 7 or 8. Ubuntu Linux works, but at this time does not provide hardware decoding for 4K hevc or VP9 ...
My point was that the thin mini ITX have single pci-e x4 slot which by pci-e spec should be providing 25W max power through the slot if I remember correctly, and GTX 1050 and most of such cards are rated for 75W. Only the full length x16 slot is rated for 75W. I think people are going around this by using a riser with a molex or sata connector providing this additional power.
I don't know however if you'd be able to power it from the thin mini-ITX itself and that might depend on the board.
That's of course IF you wanted to use thin mini-ITX to NOT play with internal power cables and don't pay for something like HD-PLEX or pico-psu. If you were to use a normal itx board then you'll end up paying for the internal power adapter for external brick. And that's what comparable to getting a normal SFX psu. Unless of course you have all that already.