It looks beautiful in TextPad and Notepad. I went down the garden path for a little while when I noticed that when I edited some aspects of my record format and saved the file from the editor it opened perfectly in Excel. So I made changes to my script to reformat the output but it had the same problem. And then I noticed that it didn't matter if I changed anything in the editor, all I had to do was save it from the editor and my problem was magically solved.
This led me to open it in HEX edit mode and found some ponderous bytes at the beginning of my file: "FF EE". A little googling led me to the answer.
By default powershell adds a “byte order mark” to the beginning of it's output. See WikiPedia
out-file -encoding ASCIIto prevent this from happening.