The RM series is of lower quality than the RMx series. Most forums recommend the RMx series. Don't skimp on the PSU. Buy the 850x, it's currently a very good price. However, 99% of the time you will get a German mains plug.
According to Corsair, Chinese capacitors are installed in the RM850 and Japanese capacitors in the RM850x. The Japanese capacitors are of higher quality, which allows Corsair to offer a longer warranty of 10 years.
Since all power supply units have the same size, they also fit into the PC case. The only problems are with special Dell cases, as they sometimes use special power supply units.
It depends on what cables you need. See the manual on page 5 to find out which cables are included with this one:
https://www.corsair.com/corsairmedia/sys_master/productcontent/RMx_2018_Manual.pdf
Basically, you have to check whether the required cables (plugs) for the CPU voltage are included, as well as the correct cables (plugs) for your graphics card.
Ciao Nico
Yes, the power supply is compatible with the mainboard. You can see it under the specifications of the power supply :)
It says:
1x 20+4-pin ATX
2x 4+4-pin 12V
It is simply written a little differently, but that works without problems :)
Greez
whitelemur
For the i version: via Corsair Link Digital you can monitor the power supply performance, switch between single and multi-rail modes and control the fan speed directly from your desktop. Whether you need this is up to you ;-)
850W should be enough, but if you want to be on the safe side, I would recommend 1000W. 1000W is also more suitable if you upgrade your components at some point. Then you don't have to replace the power supply.