Today I tried usinga separate power adapter to charge my Mac while connected to the monitor. It stops the charging sound, but I did notice my monitor wakes up once in a while and displays a message saying it's looking for signal. I wish it would just stay black until I wake up my MacBook.
It is very disheartening to hear a Dell employee saying "Dell did not test/validate the U3419W on the proprietary Apple operating system or hardware" in response to a problem that many people, including myself, are having with the monitor. The U3419W is clearly intended to function correctly when being used with a variety of devices, and Dell certainly has a responsibility to its customers to at least test basic functionality of connected Apple laptops, when those laptops represent at least 12% of the market.
So the new firmware allows the monitor to charge via USB-C when it's turned off, but unfortunately my MacBook keeps making the 'ding'-sound once regularly, as if it's being connected to a new power source. It appears the monitor doesn't provide a continuous charge.
I'm glad I no longer have to see the monitor light up and show a message that it's looking for signal, but it only solves half of the problem.
I hope this update shows Dell is listening to our complaints and takes their Mac customers more seriously and that we can expect another update soon that fixes the other issues.
I've found a solution for this, originally pointed out on the Apple forums.
The key is to go to Energy Saver preferences for the Power Adapter, disable Power Nap, and enable "Prevent computer from sleeping automatically...". This seemed to do the trick for me, no more power connected sound coming from my MacBook Pro except when I actually connect the computer to power.
That didn't work for me.
I've tried different combinations of the options:
No combination works for me - MacBook Pro (15-inch, 2017) wakes up right after I turn it off.
So there are three threads discussing the same issue now:
Any word from Dell? Should be a fix in the Monitor firmware.
The U3818DW running firmware M3B106 has a defect in the USB-C PD protocol that violates spec and causes similar sleep wake issues. This may be the same issue given M3B106 is the also the latest firmware for the U3419W and the symptoms are similar. See https://www.dell.com/community/Monitors/U3818DW-USB-Type-C-power-delivery-problem/td-p/7452974
If the U3419W is violating USB-C spec like the U3818DW is, it has nothing to do with Mac vs. PC and is a USB-C bug Dell needs to fix as they're advertising the monitor as supporting USB-C.