If you use a proxy with Basic authentication (clear-text password), you will run into problems connecting to our services when you use a Java 8.0_111 or later.
There were changes made in Java 8 Update 111, where Basic proxy authentication was disabled by default:
As the post suggest, you can enable it using a Java VM property. In DbVisualizer, open Tools->Tool Properties and select the General category. Add these lines to the Java VM Properties area:
Then click OK and restart DbVisualizer.