That is the splitter that I had that was giving me all the issues with my C8, worked fine for the C5 though. I went with the Procet PT-PTC-AT and that solved everything. It seems like everybody's setup is a little different so YMMV.
Yup - definitely a YMMV, and we're never going to track down all of the variables that result in it working for me across both C8/C8-Pro and not for others.,,though I'm not sure that anyone specifically reported on the model I used.
Other unknown (unless you open and look) is likelyhood of changes to the PCB included in splitters over time. 
A note on USB cables
So, something I've learned since the original posts is that I really lucked out with the cables I used.
When I started testing, I needed a couple of USB-C cables to loop in the USB meter. It was shortly after the holidays and my daughters had received iPads as gifts, so I grabbed the two charging cables that came with the iPads. I did my testing, and life was good. When I finished, I ended up using the iPad cables to connect the hubs to the splitters with the intention of replacing them later.
A couple of weeks ago, I got around to replacing the cables. I ordered a couple of shorter cables from Amazon... and was surprised to find that the hubs would not power up via the new cables. A little surprised, I ordered another set from a different manufacturer. These didn't work either. The abyss of another project loomed...
I ended up trying 15+ sets of cables, ranging from big names such as Apple and Anker, to inexpensive no-name Amazon only brands. Some worked, but the majority did not. Interestingly all 3 types of Apple cables I tried worked, whereas all 3 types of Anker cables did not work. Some UGREEN cables worked, some did not. No easy answers.
I'm not going to report on all the cables I tried individually as I think cables change too rapidly to make a list of much use. The take-home is that if you try a cable and the hub doesn't power up but a phone will, try a different cable.
FWIW, I ended up using these cables from an unknown brand (at least to me) because they worked, were shorter, braided and black. YMMV.
[And in case you are going to ask... my guess is that the hub doesn't draw enough power to get some of the chips in the cables to do their thing.]
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Bizarre...I just came to the topic and was going to report similar results...
I'm using the top of the line (at least most expsensive) splitter, the PT-PTC-AT version.
I initially set it up right next to the C8-Pro it's powering, using the same cables I had used w/my previous splitter. The previous splitter had worked fine, as I have noted I really only upgraded due to a little bit of FOMO. 
Then I did some unrelated (I thought) clean-up around the hub's location in the office, and suddenly my wife decided she had a better place that I should move the splitter to for aesthetic reasons. The new spot was about 6' from the original location right next to the hub. So I needed a longer USB cable. I initially tried a cable I had in my collection of cables and had used w/my phones and other devices for years w/out issues. The hub started up fine, but I began getting odd/intermittent delays in motion lighting>Z-Wave switches, and my Z-Wave blinds acted up.
I replaced the cable with an Anker cable and things have been back to normal since (maybe two weeks ago?), w/everything working normally/reliably.
So my experience echoes yours, there are definitely some potential cable issues you can run into. Interesting that the Anker cables you tried didn't work for you, Denny. Did you try the one I linked to? I assume probably not, unless you also located your splitter quite a a ways from the hub.
I should note I have a slightly "odd" configuration - I have a SonOff micro-USB switch between my POE splitter and the hub, so I can power cycle it remotely. That has been in place for years (since 2020) w/my old POE splitter and the SonOff has never caused any problems in that configuration - Z-Wave worked w/out issue w/the SonOff and C7, C8 and C8-Pro w/my old POE splitter/short cable.
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All the cables I tried were USB-C to USB-C, with the PT-PTC-AT.
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I am finding those USB switches very useful for all the USB lighting decorations that are available nowadays. I think we have 6 of them so far... Soon I will have to start checking if they go on sale.
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Yup, they are small, reliable, and pretty cheap. A nice find.
Hmmm. I wonder if that was the cause of my initial failure.....
Technology...meh. lol
S
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All the A > C cables should in theory work because there is less tech involved in sending the power. To put it simply, it just sends 5 volts all the time. Other people have reported issues using USB-C power supplies where the hub seems dead, and then an older A supply will work fine.
So probably the most reliable option would be a verified splitter with either an integrated C male cord, or if it has a female receptacle to plug your own cord in, the A style would be more reliable in the case of this hub, since it does not do any sort of USB-C power negotiations.
Of course if you already have a working C to C setup, there is no reason to change it. The only issue with it is if you change your cord you may get mixed results.
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I don't know much about USB power negotiation... yet another research project.
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Me either, I just know the USB-C does a lot more than charge stuff, it supports Thunderbolt and PD (power delivery). Also supports multiple voltages so there is some negotiation going on sometimes. I suspect that possibly some of those cords (the ones that work) are defaulting to the normal 5v if the device does not ask for anything else.
Also you know what, I think I was wrong above, not all A to C cords will work for all things. We were trying to find an A>C cord for my daughters iPhone the other day and the super basic cords that were for charging simple devices like headphones, mouse, earbuds, etc... those cords would not charge the phone. Had to use a better PD cord I had with a C to A adaptor plugged into the A style power bank. So yeah... lots of things going on.
I need to upgrade stuff with the move to C on a lot of things. I think I am going to end up buying a bunch of 3 and 6ft C<>C (PD compatible) cords and then a handful of A adaptors so we can still use our older supply blocks. That seems to work for nearly any device so far.
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What I like the most about the rise of USB-C is never having to think "Let's see, which way do I need to insert this?" and somehow guessing wrong more than 50% of the time.
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For those that might be interested, here is a good talk that covers the whole USB-C negotiation issue:
The pertinent stuff begins around 13:15, but you probably want to watch the whole thing for understanding.
If you are a patient person, this one is good as well:
This makes me want to start buying test gear.
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Awesome work, did you use one of those little usb meters like the UD18 by ATORCH or some "real" test equipment?
"Real" test equipment to me ranges in the several hundred to several thousand dollars. I didn't spend quite that much, although I wish I had spent just a little bit more.
I have a basic power meter similar unit to the one you mention, Plugable USB C Power Meter ($30), which I used for initial eyeball testing, but the sampling rate is too low (same as my eyeball ) and there is no recording capability so it could not produce data for graphing.
For the detailed testing above, I used this unit: AVHzY CT-3 ($80). It has good capabilities, including recording and a very good sampling rate. Graphing capabilities (software) are reasonable.
If I had to do it over again, I would probably choose this unit: Power-Z KM003C ($110). A little more expensive, but It's a bit more capable as a USB-C cable tester, and can also show (small) real-time graphs on the device instead of only on a PC. The cable testing capabilities would have been useful in evaluating my way out of USB-C cable hell.
Both have poor english documentation.
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That appears to be a clone of the Fnirsi FNB58 that I bought after watching Andreas Speiss' video. USB C is overly complicated and a result I sit here tangled in a mire of cables and i just wanted to charge my phone !
The USB C standard is so wacked even my FNB58 will often reboot while testing cables or power supplies.
I was aware of the lousy voltage regulation with POE adapters, so I have a Pi-power in between my hubs and use the POE to charge the batteries on the Pi-Power. I bought a pi-power with 2 x 21700 cell holder, now it appears the company has changed to a LiPo pack in the device, but you can still get the pipower at aliexpress
https://www.aliexpress.us/item/3256805914089508.html?spm=a2g0o.order_list.order_list_main.10.6aba1802ldPCL7&gatewayAdapt=glo2usa
assuming its power output is stable? I haven't had any issues with my pi-power & POE adapter on my C8
Same board with different casings. The actual board is the YK-LAB Shizuku.
This is why I wish I had splurged and bought the Power-Z instead.
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This is a great thread I've been having all kinds of z-wave instability and did some testing with a wall wart after finding this thread (was using a UCTronics Poe splitter before) sure enough it cleared right up.
Ordered a PT-PTC-BT and the hub initially fired up but then lost power and I couldn't get it back. Plugged into the wall wart again and all was well. I guess it's time to do the USBC cable dance and figure out what works?
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Afraid so. FWIW, there's a post from earlier in the year that has the cables I ended up with.
