Yes, as long as you have the 950w PSU and not the 425w one, you can power the RTX 3080 as long as you have a 1x12-pin connection for it from the PSU.  If not, 2x6-pin connectors might also work.  There's 600w to work with.  75w comes from the PCIe connection, the rest thru the 1x12-pin connection.  75w is what the MB can handle thru certain PCIe slots meant for GPU's. I can't quite explain the way they worded what you quoted, but am hopefully am of some help.  The RTX 3080 is double-height 320w total and it's specified a card can use 2x300w, which = 600w. The PCIe slots you have are Gen 3 whereas the RTX 3080 is Gen 4.0.  Due to such, there's the possibility of it running a little slower. [IMAGE] I found a 5820 running a 3080 Ti which is 350w in userbenchmark.  Also found: [IMAGE] Power connections may depend on brand: [IMAGE]  
Hello,   Currently my Dell Precision T5820 has Quadro P4000 with 950W power supply,  I would like to upgrade it to RTX 3080. I'm confused that in T5820 features it says max 300watt per card in total of 600watt per pci slot. Does it mean my pci slot is not providing enough for RTX 3080? Because 3080s seem to require at least 350 watts. Or maybe I am misunderstanding something. Thank you for your help.    
Dell Precision Tower 5820 XL GPU Upgrade to RTX 3080