In this case, if you want to use the 3 vga at the same time, it would be interesting to use a source with approximately 1000w as @rdluffy said. Corsair RM 1000x, HX1000 or EVGA 1000w SuperNOVA, are good examples that you could buy.
- If you happen to know any link where I can find all such details regarding eth mining [keeping in mind as beginners] please do share here.
I know this site, where it simulates approximately how many watts you will need to use, in my opinion it is very useful.
ps: use this site only to be able to rely on approximately how many watts you will use.
https://www.coolermaster.com/power-supply-calculator/I hope I have been helpful