How to combine Folders

Sky571 - Sorry, one other question while I try to work through how to do this, is there any other way to identify the 2 sets of files other than which folder they are in and their delimiter? In other words, do they follow different file naming conventions or have different file extensions?

Sky571 - I don't quite have my example working yet, but here is what I am thinking.

Your main query in a Folder query basically looks like this:

let
    Source = Folder.Files("C:\temp\powerbi\csvs"),
    #"Filtered Hidden Files1" = Table.SelectRows(Source, each [Attributes]?[Hidden]? <> true),
    #"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File", each #"Transform File"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File", Table.ColumnNames(#"Transform File"(#"Sample File"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"column1", Int64.Type}, {"column2", Int64.Type}, {"column3", Int64.Type}, {"date", type date}})
in
    #"Changed Type"

So, you could do this:

let
    Source1 = Folder.Files("C:\temp\powerbi\csvs"),
    Source2 = Folder.Files("C:\temp\powerbi\csvs1"),
    Source = Table.Append(Source1,Source2),
    #"Filtered Hidden Files1" = Table.SelectRows(Source, each [Attributes]?[Hidden]? <> true),
    #"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File", each #"Transform File"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File", Table.ColumnNames(#"Transform File"(#"Sample File"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"column1", Int64.Type}, {"column2", Int64.Type}, {"column3", Int64.Type}, {"date", type date}})
in
    #"Changed Type"

That part gets all of your files being fed through the same process. Next you have your Transform Sample File function that looks like this:

let
    Source = Csv.Document(Parameter1,[Delimiter=",", Columns=4, Encoding=1252, QuoteStyle=QuoteStyle.None]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true])
in
    #"Promoted Headers"

So what I am thinking is that you add a Parameter2 to the Helper Queries folder and you set that when you call the function. And you can tell what delimiter to set for this parameter because of what folder your file is coming from, so the Transform Sample File would end up looking like:

let
    Source = Csv.Document(Parameter1,[Delimiter=Parameter2, Columns=4, Encoding=1252, QuoteStyle=QuoteStyle.None]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true])
in
    #"Promoted Headers"

As I said, I don't quite have it all working just yet but figured I'd explain what I am thinking and maybe you can figure it all out before I can or maybe ImkeF and edhans or someone better at Power Query than I can step in and wrap it up. But, seems definitely possible to me.