Combine power query output table with manually maintained column in one excel table

Hi Riny_van_Eekelen, I am running into what I'm sure is a dumb mistake but I can't figure where I'm going wrong - I'm attempting this process but keep ending up with 3 tables instead of two when trying to follow your steps

1. "Create First Table (Source)" - Table 1

2. "Query it and load to...name (Source_2)" - Table 2

3. "Query table (Source_2), now including Notes" - Table 3

It seems that following the process I should only be ending up with two tables Source and Source_2, but again I keep ending up with 3 - Any help would be appreciated, thanks! 

Riny_van_Eekelen 

I am a bit of novice but am able to follow. In your example, both sources are existing tables. Is it possible to replicate this if the original source is a file in a folder? 

Riny_van_Eekelen , I modified a bit, hope self-explainable

let
    Source  = Excel.CurrentWorkbook(){[Name="Source"]}[Content],
    Source3 = Excel.CurrentWorkbook(){[Name="Source3"]}[Content],
    SourceColumns   = Table.ColumnNames(Source),
    SourceColumns3  = Table.ColumnNames(Source3),
    FirstTime = List.ContainsAll(SourceColumns, SourceColumns3),
    Return = if FirstTime then Source else
        Table.Join(
            Source,  SourceColumns,
            Source3, SourceColumns
        )
in
    Return

Another table in your file.