Right they’re two very different errors. One is PSU related I reckon, in the c case of the graphics card, and the other is motherboard battery.
First thing to do is check the rails on that powersupply of yours. There are several freeware programs that do this such as Speedfan , I use A.I Booster/Asus Probe II on mine. That will tell you how your PSU is coping with the system load, the voltages across the rails should be a max of 3% off the guideline voltages i.e 3V, 5V and 12V.
Next, if the PSU turns out to be alright its disassembling time. Try booting up with some components disconnected and see if your getting the same errors. If this leads to the same result then its the last issue I’d start looking at…
The CMOS battery on your mobo might be gone but for a Gen 3 XPS it would be strange if that was the problem, if it turns out to be this ring Dell, plain and simple.
Overall it sounds like a PSU problem though pretty must just not giving your system enough power when it needs it. Oh and as a matter of interest what temps do you have when your pushing the system?