In SQL i'd normally use a cross join to create the cartesian product of all values - basically, joining every row with every other row. I'm not sure this is possible in power query, but you can trick it by creating a custom column for all input tables that has the same value, then doing some joins on these columns (all the values are the same so every row will join with every other row)..
I've knocked together the power query here (might be a more effecient way but this seems to work):
let
//Our source tables, replace with whatever, just make sure the Colum header is "Val"
X = Table.FromList({"a","b","c"}, null, {"Val"}),
Y = Table.FromList({"A","B","C"}, null, {"Val"}),
Z = Table.FromList({"1","2","3"}, null, {"Val"}),
//Adding custom column for join
X_2 = Table.AddColumn(X, "JoinCol", each 1),
Y_2 = Table.AddColumn(Y, "JoinCol", each 1),
Z_2 = Table.AddColumn(Z, "JoinCol", each 1),
//Join all the tables together
Join_1 = Table.NestedJoin(X_2,"JoinCol",Y_2,"JoinCol","Y"),
Join_2 = Table.NestedJoin(Join_1,"JoinCol",Z_2,"JoinCol","Z"),
//Remove the custom column
RemoveCol = Table.RemoveColumns(Join_2,{"JoinCol"}),
//Expand out our Y and Z columns
ExpandY = Table.ExpandTableColumn(RemoveCol, "Y", {"Val"}, {"Y.Val"}),
ExpandZ = Table.ExpandTableColumn(ExpandY, "Z", {"Val"}, {"Z.Val"}),
//Rename the columns to something we expect
RenameColumns = Table.RenameColumns(ExpandZ,{{"Val", "X"}, {"Y.Val", "Y"}, {"Z.Val", "Z"}})
in
RenameColumnsThis outputs a table like this:
X,Y,Z
| a | A | 1 |
| a | A | 2 |
| a | A | 3 |
| a | B | 1 |
| a | B | 2 |
| a | B | 3 |
| a | C | 1 |
| a | C | 2 |
| a | C | 3 |
| b | A | 1 |
| b | A | 2 |
| b | A | 3 |
| b | B | 1 |
| b | B | 2 |
| b | B | 3 |
| b | C | 1 |
| b | C | 2 |
| b | C | 3 |
| c | A | 1 |
| c | A | 2 |
| c | A | 3 |
| c | B | 1 |
| c | B | 2 |
| c | B | 3 |
| c | C | 1 |
| c | C | 2 |
| c | C | 3 |
