How much power do I need for my pc?



I'll stick to the 1x8 gb ram (for if I want to upgrade later, since my MB has only 2 RAM slots)
The power supply you mentioned isn't in the store in my country ( I wont order parts online because it's more expensive than just buying them in my country (taxes :/))
Now I'm thinking of getting this power supply -

https://pcpartpicker.com/product/823H99/thermaltake-smart-rgb-500w-80-certified-atx-power-supply-ps-spr-0500nhfawu-1

Is 500 w too much? Or should I get this one -

https://pcpartpicker.com/product/rLW9TW/corsair-power-supply-cp9020052ww

They're roughly the same price.
 


Sadly, that is too expensive for me.
I was thinking of buying this psu -
https://www.instar-informatika.hr/napajanje-thermaltake-smart-rgb-500w/0151392/product/

 


mixing RAM is always a gamble. it might work, or more likely it will not, there is a reason RAM is tested and sold in matched sets. getting 2 sticks (matched) now will give you the performance dual channel offers. in all likely-hood you would need to replace the single stick later anyway - as matching RAM is tricky.
I have had RAM from the same company made 1 module apart (serial numbers 1 apart) not work together.
unless RAM is given to you I do not suggest mixing ram sticks, replace not add to.

the thermaltake would be marginally better than the VS. I wish you could get the cx550 but its extra