also this have been bothering me for a while. might be a stupid question but don't laugh. what does "on/from/out of the wall" means?
Depends if you dual mine or not. I have a 6 card rig with 4 RX 480/580, 1 RX 570 and one 1080. I use an EVGA 1000W P2 with 6 PCI-E connectors for the VGA power inputs only and use an EVGA 750W P2 for the motherboard and all the risers. Dual mining the VGA's draw ~805W and 360W for the motherboard and risers. If you dual mine, you might be able to get two 850W to work, but I would go with the 1000W so you have enough PCI-E connectors for the cards.
also this have been bothering me for a while. might be a stupid question but don't laugh. what does "on/from/out of the wall" means?
Yes, two 750 watts PSU's should be fine as you should be around 900-950 watt total system draw.
I assume you are referring to a rigs power draw when you refer to "at the wall". It usually indicates the user is referring to the fact they are citing figures measured using a power meter placed in-between the PSU's AC input and the outlet itself so as to measure the true total system draw. This is different than others who may cite simply the power reading obtained from software, such as GPUz and its power draw reading. The problem with software readings is they are usually incomplete and only measure part of the total consumption.
Since an "at the wall" measurement includes all the components of a mining rig (GPU, CPU, RAM, Mobo, PSU, HDD or SDD, etc.) you will get the most accurate figures for determining your net profit if you pay for electricity.
thanks both of you. that answer my questions perfectly.