TL;DR: (Scroll down to bottom two questions)
I have found dozens of "solutions" on the Raspberry Pi 3B which have worked for people and not with my 3B+.
I suspect that there is a very specific problem with the "+" version, due to Ubuntu's wiki (https://wiki.ubuntu.com/ARM/RaspberryPi) stating:
Raspberry Pi 3 B+ (2018) functionality is not yet available with these images.
Raspberry Pi 3: ubuntu-18.04-preinstalled-server-armhf+raspi3.img.xz (4G image, 296M compressed) Updated 2018-04-28 (18.04 LTS)
Raspberry Pi 3: ubuntu-16.04-preinstalled-server-armhf+raspi3.img.xz (4G image, 252M compressed) Updated 2018-04-21 (16.04.4 LTS)
I have followed numerous guides on the 3B and a few guides specific to the 3B+ (not the 3B) and none of them have worked. I have flashed several "special 3B+" images onto my SD card and nothing works.
I have tried three different brands of cards, a total of 10 cards. I have tried four different USB power adapters ranging from 0.5A to 3.5A.
The furthest I have gotten is constant rainbow screen, although 90% of the time there was no HDMI signal (100% failure with the latest firmware from GitHub, which is really confusing to me).
As for the other indicators: Red light is constantly on (when powered). No other indicators on the Pi. When I did plug other devices in: Keyboard does not light up (even on powered USB splitter), LAN lights both dimly lit but DHCP never sees anything in that port.
I literally have setup two virtual machines to assist in my efforts, I have compiled all kinds of different projects including the u-boot for ARM in both 32 and 64-bit.
After spending two days (over 30 hours) working on this, I come with two questions:
1: Is it possible to get Ubuntu Server (64 bit) onto my Raspberry Pi 3B+?
2: If so, what are the specific steps?
I would really appreciate any help - I usually do not have problems like this.