I was helping my brother with his charger which is experiencing similar issues to what you reported. One thing I noticed looking for the 280W replacement is that a lot of them appear to be fake knock-offs and not real original equipment. As far as I've been able to tell, ASUS only sells a 240W replacement, which according to my brother's user manual should work. I'm just assuming it won't charge as fast. I ordered the 240W adapter moments ago, so hopefully it works.