OK.
That picture shows that the monitor is getting power when attached to the new MBP. It just isn't getting signal. I was under the mistaken impression that the monitor was showing nothing at all, as if it did not have its own power source, and was not getting power from the MBP, either.
That first link leads to a page for several monitors. Yours is appears to be the J5.
The J5 is a 17.3" monitor with 3840x2160 pixel resolution and a 60 Hz refresh rate. It has two USB-C inputs and a HDMI input, plus a downstream Micro USB-B port. The specifications say that it does not have a built-in battery – and that its rated power is 17 watts. The monitor has an IPS panel and 100% coverage of Adobe RGB – both good specifications that don't matter for the purpose of troubleshooting here.
3840x2160 @ 60 Hz is bog-standard and well within the capabilities of your MacBook Pro, whether you use one of the MBP's USB-C ports, or use the MBP's HDMI port.
Here's the manual .
In Chapter 3 of the manual, under Type-C signal transfer, and again under HDMI signal transfer, they say
"Note: 4K monitor needs higher voltage power, for a more stable power supply, it is recommended to use our original PD adapter to power."
In Chapter 6 of the manual, under Q&A, they say
"Q: The monitor keeps switching and flicker, although it connected to outlet for extra power supply.
A: This situation is generally caused by insufficient voltage. Please check whether the factory-packed cables are used, and then check whether an external PD power supply is used. The power consumption of 4K monitor is relatively larger, and an external PD power supply is required."
They also say that the monitor requires at least a 15W power supply, but that their power adapter provides 30W, so that if you use a power bank (external rechargeable battery), one "with output above 30W is recommended."
Part of USB-C Power Delivery is that the power supplier negotiates with the power consumer as to what voltage to offer. The original standard allowed power transfers of up to 5A at up to 20V (up to 100W); the current one allows power transfers of up to 5A at up to 48V (up to 240W).
If I look at the fine print on the bottom of a 29W Apple USB Type-C power adapter, I find the words "Output: 14.5V === 2.0A (USB PD) or 5.2V === 2.4A." Both my MacBook and my iPhone charge off this adapter, but if either was picky enough that they would not accept anything less than 20V, they would be in trouble.
So the highlighted parts of the monitor manual raise some follow-on questions:
- What "higher voltage" does the monitor expect?
- What voltage is the old MBP offering?
- What voltage is the new MBP offering?
- Could the voltage that the new MBP is offering be high enough to let the screen come on and display that "No signal" message, but not high enough to let the electronics to receive a signal work properly?
