Reversed Polarity on DC Power Supply. Can I replace Fuse/Diode on MB?

Check if the power supply is dead. You can always pick another travel adaptor. As far as I know, laptops as the voltage is given by the power supply, don't use any fuse. It's quite difficult to diagnose smd problems specially on laptops, because the components are pretty close one to the other, but you can check if any part is burnt by having a look to it.

I know it’s late, but I have the same problem, and feel obligated to document the process for anyone else. I reversed the polarity, and have precisely the same symptoms as you described. I decided to run the power backwards again (can’t kill it twice, I hope) and felt around with my fingers for any components that were heating up (MOSFETs tend to fail short circuit). I noted the chips shown heated up (see attached) and so I will try to replace them, and see if the problem is resolved. I’ll report back with the results. (Ignore the wires and glue, the DC socket broke, and this is a temporary bodge to feed power to the laptop.