Hello, thegalah!
I've built a few of these boards before (even last week I had quite a few) and before that a ton of the Z270i and here are some things that I have learned about the board for no-power on scenarios.
1. The HDPLEX 160 / Dynamo Mini is more than enough to power on any system. I ran a 1070 system off a HDPLEX 160 for about a month during testing. You'll draw a max of around 40w at startup, and it will fall below that in Windows. You can even run a 1070 off a Dynamo mini for a short period before it will cut off, so startup is not a problem. As a side note, I think it is 100% fine for your system.
2. I don't know if you have a MINI, but plugging in the PCIE Key upside down will cause a no-power on with this board and most GPUs.
3. This board will output the Aura RGB LEDs even if it is dead. I have experienced this before and it was a doozy to troubleshoot.
4. This board will output the Aura RGB LEDs if your CPU is dead. Also hard to troubleshoot. 
5. The amber light by the GPU will come on for a majority of no-boot situations. What you are looking for are the white or red LEDs near the memory slots at the top. If those aren't lighting up, you may have a defective board. I had to send one to ASUS and they sent back a note "NO POWER (Debug Card No Action) [Power on/off fail].
6. Believe it or not, having your M.2 card plugged in poorly can trigger this. I have been sent customer builds to work on and sometimes they forget to put the standoffs on, which can prevent a no-boot for some reason.
7. User error. Forgetting to plug the 4+4, or GPU power cable, or ON/OFF cable correctly. It happens.
8. Installing the motherboard but not bending the I/O shield ground tabs back so they stick inside your USB3 port.
But I saved the probably cause for last. The Dell 330 brick. If you didn't buy a genuine Dell brick but bought one off eBay or Amazon the most common issue with them is poor startup/no startup due to the barrel connector not mating appropriately with the HDPLEX/KMPKT DC jack.
Taken from my MINI FAQ:
My Dell 330 and HDPLEX 400 lights shut off and won't power on!
[SPOILER]There is a certain batch of Dell adapters (perhaps grey market or non-genuine) that have barrel plug issues.
The symptom is when you plug the AC cord to this Dell adapter and then connect the Dell adapter to the HDPLEX 400W the Dell adapter power indicator light will go off (and sometimes the HDPLEX light too) and the PC will not power on.
The solution is to FIRST connect the Dell to the HDPLEX 400W and THEN plug the AC power cord into Dell adapter, and FINALLY plug the cord into the wall. This is good practice for electronics anyway.
Several customers have solved this issue by purchasing their powerbrick from a different channel (like Dell.com).
Quote:
"Well it turns out the new Dell adapter did fix my problem.
Comparing the new unit to the old, the only difference I really notice is the old one has a tiny bit of roughness where the black plastic ring meets the metal of the DC connector. So I'm just guessing here, but maybe the metal there is causing some sort of spark as it makes contact."[/SPOILER]
Special thanks to Larry for helping me solve this problem.
