If you just Out-File or > filename in the Powershell that ships with Windows (not the most recent cross-platform powershell), then
Get-ChildItem * | Out-File filename.txt
outputs UTF16 with a BOM at the start. If you want plain old ASCII or UTF8, use -encoding
Get-ChildItem * | Out-File -encoding ASCII filename.txt
Get-ChildItem * | Out-File -encoding UTF8 filename.txt