The PSU in the typical gaming PC is often overkill. The HX1000i is a good PSU but it is overkill for a single elite graphics card. The RM650 on the other hand is a far more practical choice. Some high-end power supplies have monitoring ability but low cost appliance monitors are $10 postage paid from Chinese merchants.
There are lots of ways to measure power draw or load. The HX1000i has a USB port for monitoring. When SLI/CFX was more common place, this is where the HX1000i thrives. Today however, the dual card option has largely been abandoned by both AMD and nVidia.
To load the machine the popular Furmark is selected which can be run in a window so that power monitoring software can be seen.
The RTX 2080 is rated at 215W which is slightly above the average for recent cards in use. The RTX 2080 features a boost feature which increases the clock speeds. The R5 3600 is a 65W CPU which also has a boost feature.
Opportunist boost that is dependant on the thermal load. Video cards and CPUs are now both offering this capability. The advantages of high-end cooling can afford a slight increase in maximum performance.
At idle the machine draws a bit more than 120W at the wall. The efficiency varies from 87% to 90% depending on load. With Furmark running the load rises to around 300W at the wall. This demonstrated conclusively that the HX1000i is overkill.
The new RM line: RX650, RM750 and RM850. Clearly with the existing hardware, the RM650 is quite adequate. Even with the higher power draw of the R9 Fury, GTX 690 and RTX 3080, the RM650 can handle them easily.
The big advantage of the RM650 it the higher efficiency at lower loading. The 5V standby is well provisioned and it is very efficient which makes the PC a good choice for charging mobile devices.