Ok, after some investigation, I wired this 12V DC-19.5V DC adaptor and connected it to laptop with intercept to monitor voltage as its connected.1-Laptop battery fully charged to start with from AC adaptor connected with power on. No problems.2-Power failure-Load shedding SA.3-I connect 12V/7AH fully charged battery to DC-DC adaptor. Connected it settled at 19.11=19.13Volts.Note:It does not like 20V, theres a soft sound you wont hear with noises in the room.Quickly reset it to 19V=Latop happy no sounds.4a-This is not a 100% selution due to the 3rd wire between Dell Adaptor and Laptop=Yello=Communications wire. The laptop ask adaptor for more or less power depending condition of battery if I understand this correctly on 3rd lead.4b-However the result now is I have the effect of having a battery that seems better than a new one, as it slowly discharge. I am probably safe here not overcharging it-19.13V. This totally acceptable to me, it seems I can go on for a few hours on a small 12C/7Ah sealed lead acid battery, same as the Fibre box and Router has and they last very long. So I am very happy with this.5-Will see if it has any long term effects.6-When power comes back, I switch off the 12V battery suply, plug it out, and reconnect the original Dell adaptor to laptop, and that is how battery gets fully charged again.7-Note:Before this I ran a small UPS from this 12V/7AH battery, it does the job, but the UPS gets warm, I have to reset it every few minutes without battery going flat(11.5V). This operation although it charges the laptop correctly, is a pain, I dont like it. The DC-DC adaptor is a far better selution energy wise compared to the UPS, or an inverter for that matter   DC-AC-DC=Waste of energy for this case.8-So does the DELL Company wants to come up with a 12VDC-DC19V charger that uses 3 wires and communicates correctly......I am sure a lot of people may like it for using in cars etc or at home or at remote holiday camping having the energy contained around DC.
Universal power adaptor: Will this work with Dell Inspiration 13 5000 series-?Link=[URL]
I want to use a universal 12VDC car Adaptor to 19.7Volt DC for this laptop due 
power cuts