The question says it all.
The specialty in my case is that the current working directory is not the location of the jar file but c:\\Windows\\system32 (
c:\\Windows\\system32
To get Launcher.class.getResourceAsStream("/../config.xml") to work, you need to add its path to the Class-Path entry of the JAR's MANIFEST.MF file. This is the normal practice.
Launcher.class.getResourceAsStream("/../config.xml")
Class-Path
MANIFEST.MF