Connection Issue

I'm using a Powershell script to connect to a remote 16.3(windows) version
of the DB.

Add-type -path 'C:\Program Files
(x86)\PostgreSQL\Npgsql\bin\net451\Npgsql.dll'

# Define connection strings for MS SQL and PostgreSQL
$pgsqlConnectionString =
"Host=xxxxxx;Port=5432;Username=xxx;Password=xx;Database=xxx;"

# Create connection to PostgreSQL
$pgsqlConn = New-Object Npgsql.NpgsqlConnection
$pgsqlConn.ConnectionString = $pgsqlConnectionString
$pgsqlConn.Open()

When this statement hits I get an error:

Exception calling "Open" with "0" argument(s): "Authentication method not
supported (Received: 10)"

Any ideas?

Thanks.