let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Changed Type" = Table.TransformColumnTypes(Source,{{"some Hex", type text}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each Text.From(Expression.Evaluate("0x" & [some Hex])))
in
#"Added Custom"
=DECIMAL(B2,16)
=LET(L,LEN(B2),seq,SEQUENCE(L),SUM((FIND(MID(B2,seq,1),"0123456789ABCDEF")-1)*16^(L-seq)))