Let me correct a few things… HFS+ & APFS file systems both use GUID as their drive format. High Sierra installer could be setup before you run it so not to alter the SSD drive’s file system to APFS (HDD’s where not altered). But once upgraded you can’t undo it without a complete wipe of the drive. In the case of Mojave All internal boot drive are converted now! I have not found a way to prevent it.
APFS is very drive intensive unlike HFS+ In addition, SATA interface dialog is limited in its queueing (only has four) unlike PCIe/NVMe which not only being a faster I/O also has a very deep queue 16/32 depending on the lane width.
So the simple answer is older SATA based systems should stay with Sierra (HFS+) and as High Sierra has issues! I don’t recommend it (which is why you want to stick with Sierra), Mojave is by far better as a MacOS on PCIe/NVMe SSD’s!
As far as external drives… None of the OS’s alter them magically (unlike HS & M does on the internal boot at the time of upgrade). But if you are trying to boot up with an external drive which is using an older OS than you have on your system you can encounter issue of not being able to access your internal drive as the external boot drives OS may not have the needed means to read/write to the APFS file system.
If you take out your internal drive hoping to recover its data to a Windows or Linux system neither have the ability currently to access APFS! Windows does have a driver you can buy from either MS or 3rd parties to access HFS+ drives.
OK lets get back to your USB port issues. Some devices require a driver by the device vendor to work. Mojave is the last MacOS to support 32bit apps and drivers. You’ll want to review your apps and drivers to get newer versions or just remove them when you jump to Catalina this fall.
I would recommend getting one of these: USB-A & USB-C power meter which will offer both voltage and current draw.
If the ports are working from a power perspective I would suspect your logic board has issues. As no matter what MacOS you are using the OS as well as Disk Utility should have no issues accessing FAT16 or 32, NTFS or exFAT external drives.
As you didn’t tell us what the device is you are having problems please tell us.
References:
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