How do you call msdeploy from powershell when the parameters have spaces?

Using the technique from Keith's answer to How to run exe in powershell with parameters with spaces and quotes question you linked to, running echoargs -verb:dump -source:appHostConfig=$sitename -verbose gave me this output:

Arg 0 is <-verb:dump>
Arg 1 is <-source:appHostConfig=default>
Arg 2 is <web>
Arg 3 is <site>
Arg 4 is <-verbose>

This would explain the invalid argument of appHostConfig=default that msdeploy was seeing.

Running echoargs -verb:dump "-source:appHostConfig=$sitename" -verbose, with $sitename = "default web site", appears to result in the desired arguments:

Arg 0 is <-verb:dump>
Arg 1 is <-source:appHostConfig=default web site>
Arg 2 is <-verbose> 

Though from your list, it appears that this did not work for you.

Another method you might try is building up the list of arguments in an array, which powershell can automatically escape. For example, this gives the same output as above:

[string[]]$msdeployArgs = @(
  "-verb:dump",
  "-source:appHostConfig=$sitename",
  "-verbose"
)
echoargs $msdeployArgs

Just adding another way in case it is helpful to anyone:

Invoke-Expression "& '[path to msdeploy]\msdeploy.exe' --% -verb:sync -source:contentPath=`'$source`' -dest:contentPath=`'$dest`'"

"--%" is new to powershell 3. From here: "You simply add a the --% sequence (two dashes and a percent sign) anywhere in the command line and PowerShell will not try to parse the remainder of that line."

Found a working solution and easy fix. Reference: http://answered.site/all-arguments-must-begin-with--at-cwindowsdtldownloadswebserviceswebservicesidservicepublishedwebsitesidservicedeploymentidservicewsdeployps123/4231580/

$msdeploy = "C:\Program Files\IIS\Microsoft Web Deploy V3\msdeploy.exe"
$msdeployArgs = @(
"-verb:sync",
"-source:iisApp='Default Web Site/HelloWorld'",
"-verbose",
"-dest:archiveDir='c:\temp1'"
)
Start-Process $msdeploy -NoNewWindow -ArgumentList $msdeployArgs