DynParamBySwitch.ps1

# Get-Inventory -Server -IPAddress 1.1.1.1 -Credential (Get-Credential)
# Get-Inventory -Storage -WebServiceEndpoint https://a.b.c -OAuthToken XXXXX

function Get-Inventory
{
    [CmdletBinding()]
    Param()

    DynamicParam
    {
        $ValidateSet = 'Server', 'Storage', 'Bar', 'Baz'

        $BaseDP = $ValidateSet | ForEach-Object { 
            @{
	    	Name = $_
	    	Type = [switch]
                Parameter = @{
                    Mandatory = $true
                    ParameterSetName = $_
                }
            }
        }
        
        $ExtDP = @(
            @{
	    	Name = 'IPAddress'
	    	Type = [ipaddress]
                Parameter = @{
                    ParameterSetName = 'Server'
                }
	    },
            @{
	    	Name = 'Credential'
                Type = [pscredential]
                Parameter = @{
                    ParameterSetName = 'Server'
                }
            },
            @{
	    	Name = 'WebServiceEndpoint'
	 	Type = [uri]
                Parameter = @{
                    ParameterSetName = 'Storage'
                }
	    },
            @{
	    	Name = 'OAuthToken'
                Type = [string]
                Parameter = @{
                    ParameterSetName = 'Storage'
                }
            }
        )

        $DynamicParameters = $BaseDP + $ExtDP

        # Create the dictionary
        $RuntimeParameterDictionary = New-Object -TypeName System.Management.Automation.RuntimeDefinedParameterDictionary

        foreach($dp in $DynamicParameters)
        {
            # Create the collection of attributes
            $AttributeCollection = New-Object -TypeName System.Collections.ObjectModel.Collection[System.Attribute]

            # Create and set the parameters' attributes (Parameter, ValidateSet)

            # [Parameter(ValueFromPipeline, ValueFromPipelineByPropertyName)]
            $AttributeCollection.Add(
                (New-Object -TypeName System.Management.Automation.ParameterAttribute -Property $dp.Parameter)
            )

            # [ValidateSet()]
            if($dp.ValidateSet)
            {
                $AttributeCollection.Add(
                    (New-Object -TypeName System.Management.Automation.ValidateSetAttribute -ArgumentList $dp.ValidateSet)
                )
            }

            # Create and return the dynamic parameter
            $RuntimeParameter = New-Object -TypeName System.Management.Automation.RuntimeDefinedParameter(
                $dp.Name,
                $dp.Type,
                $AttributeCollection
            )
            $RuntimeParameterDictionary.Add($dp.Name, $RuntimeParameter)
        }

        # Return dicitonary
        $RuntimeParameterDictionary
    }

    Process
    {
        $PSBoundParameters
    }
}