To conclude this thread... After I initially posted, within 30min Dell Social Media team messaged me asking for details and promised the 3rd appointment will work out. That was very good. This morning, got a phone message to confirm the appointment, and got an email with tech's contact. Interestingly, the phone message said my appointment was 10am to 2pm, and the tech's email said 12-2pm... The tech person turned out to be Luis again. I messaged him asking if he has the part in hand, he replied, he is still waiting for FedEx... Fortunately, right before the appointment window, he got the part and came on time. The rest of the repair was fine. So, my observations are, I like all the customer facing WhatsApp chat and the Social Media team responses... all the "talk" is really very good, but the "action" part is lacking. Do better next time, Dell. But I hope I don't need a next time. 
Your warranty service calls are terrible!! 2 times now for the same computer, your tech didn't have the part on the day of the appointment, and had to schedule. I am now waiting for the 3rd appointment!! So far so good... That was pretty disappointing, you didn't have the part, didn't tell me, only informed me when I asked after the appointment time was over. Is that good customer service? Really?? There is no validation check to see if critical fields are filled in when your company sends emails out?!? Dell, really now, 2 times, you didn't have the part ready, and you scheduled and confirmed appointments with me?!?  Don't you think you should confirm the part is available, days before the appointment, or at least the night before the appointment, instead of wasting my time?  Why do you tell me you can't come after the appointment windows expired or just right before, and only when I asked?  Don't you think your customers have lives to live and should not be expected to rearrange our lives around your incompetent service calls? From a scale of 1 to 10, how do you rate your own service?  
Terrible service call experience