I've seen articles in C# and some other languages that explain how to achieve what I'm looking for but I don't know how to convert them.
The following link explains how to get the answer:
How can I get the drive letter of an USB device?
Win32_DiskDrive-> Win32_DiskDriveToDiskPartition -> Win32_DiskPartition -> Win32_LogicalDiskToPartition -> Win32_LogicalDisk
The answer by GEOCHET explains also explains how to achieve the answer but again, not in PowerShell: How to find USB drive letter?
Try:
gwmi win32_diskdrive | ?{$_.interfacetype -eq "USB"} | %{gwmi -Query "ASSOCIATORS OF {Win32_DiskDrive.DeviceID=`"$($_.DeviceID.replace('\','\\'))`"} WHERE AssocClass = Win32_DiskDriveToDiskPartition"} | %{gwmi -Query "ASSOCIATORS OF {Win32_DiskPartition.DeviceID=`"$($_.DeviceID)`"} WHERE AssocClass = Win32_LogicalDiskToPartition"} | %{$_.deviceid}
Tested with one and more than one USB device plugged-in.