I picked up a tricked-out Dell XPS 17 laptop a few years back. It worked great until it stopped recognizing my genuine Dell PS (just outside of my warranty period too... which SUCKED). That in turn caused the thing to run at a REDUCED clock speed and REFUSED to charge the battery. After a bit of digging, it turns out that there is a 1-wire protocol between the PS and the laptop. If that goes down, you are left with a slow running, paperweight. Dell doesn't like you running after-market PS on their devices, but also screws legitimate customers because the engineering behind it sucks.
The thing that irritates me the most is that I *know* this is just a software check in the BIOS. If they would release an unlocked BIOS, I'd be good to go.
Needless to say, I've never bought another Dell since then. I've been extremely happy giving ASUS my business instead.