Dell warranty covers only the original parts that it came with.

Why don't they say that, if that's what they mean!  The real question is about the real maximum amount of memory the pc can take, and not just an answer of Dell doesn't support it.

Dell not supporting something usually means they didn't test that particular configuration. They would have tested 24GB RAM successfully and failed higher levels in the preliminary hardware. Over time hardware can become upgraded because of being supplied with improved parts and Dell will not retest. Over the years there have been a number of Dells that were able to handle more RAM than Dell "recommended". One in particular was the E 1û05 laptop that was sold with 2GB. Early models usually wouldn't handle more, but later builds worked fine with 4GB. 

If you need warranty service, you probably should degrade it back to 24GB. They probably would insist the problem is due to the extra RAM.

Thanks KirkD. That is the clearest response I've seen about this topic on any thread.