I've always wanted to build a potent mini-ITX system and took a leap of faith with the Lian Li Tu 150 case. It's the only small mini-ITX case I've found thus far that can accommodate a triple slot GPU not to mention the extra long length. I have the PC up and running and it's been fantastic so far. Still running stability testing and tweaking. I'm currently using an EVGA 650GM sfx power supply. Running RealBench with a 9900K at 4.8ghz and 2080 Ti FTW3 Ultra at stock for now, HWInfo shows total power draw of 428 watts. So you *can* get away with a 650 watt power supply here if you aren't doing ultra intense tasks. I have a non-recalled Corsair SF750 on order that I plan to swap in case I need more juice. 
 
It isn't pretty but the best I can do re: cable management due to the small size and short cables. 
 
 

DeadlyMercury
Well, my system (same 9900k+2080ti) with overclock, dozen of fans etc consuming about 550w in heavy games or benchmarks like 3dmark/heaven/superposition, so yeah, you can live with 650-750w psu.
In stress test though (gpu+cpu avx2) it goes up to 800w.
 
Another story is cooling this thing... But there is no place for cpu plus gpu aio as I can see.

Cooling is enemy #1 haha. Playing some F1 2020 and GPU temp hits 82C with an offset of +100 (2025 or so mhz). Roughly 10 to maybe 15 degrees hotter compared to my regular ATX build. I have 1x 120mm case fan for intake and another for exhaust. My CPU is OC to 4.9ghz which is more than I had hoped for coming from my ATX case with great air flow. I don't do any regular benchmarking or the like. 
 
Am definitely putting in the 750 watt psu when I receive it, though. Should be fine for office work and gaming which is all I use the PC for. 

Flybye
That is a very tight case!  And I'm not talking about the slang tight either, lol.
 
I'd be too tempted in drilling the side cover out and installing a 150-250mm fan.  Won't be pretty, but it would sure be functional. 

It is very tight. I really had to cram the fans onto the NH-D15S cooler but it does fit and works perfectly. I did some more CPU voltage tweaking and all around fan curve tweaking so things are a bit cooler. In-game (F1 2020) my GPU tops out at 80C with a +100 core offset (1995 - 2025 mhz range). I don't want to mod this great looking case yet but that's a great idea. We'll see what the next gen of GPUs are like size-wise. I will go with a dual fan / dual slot GPU next time which will give me space to install 2x 120mm fans for intake at the bottom of the case, which should really help temps. I'm tempted to sell / trade my FTW3 Ultra for a smaller 2080 Ti to do just that. I am very impressed with this case, a dual slot GPU really is ideal for it though. 
 
Running my CPU at 4.9ghz without AVX offset and GPU at +100 core, my Kill-a-watt showed 550 watt maximum usage during F1 2020. Not the most demanding of games, but the 750 watt power supply will make me feel better.