The power supply on my Zbook workstation has always been warm/hot to the touch if working computer hard so probably not unusual. If you don't get any "burning or melting plastic" odors there is likely not a problem and that heat generation is one reason that laptops typically do not have internal power supplies. Keep in mind that many of the higher end adapters are supplying 100-150 watts of power and thing about how hot even a 60 watt bulb gets. Not necessarily a perfect comparison but gives you a baseline to think about.
If you find the information provided useful or solves your problems, help other users find the solution easier by giving kudos and marking my post as an accepted solution.