Can I use any PSU??

Smelyn

I am thinking of getting asrock atx motherboard (b450 pro4) with a AMD Ryzen 5 2600 and a GRx 1660 Super. I’m new to building Pcs so i’m gonna post more questions.

BubbleMax

Well you could start by googling roughly the average power draw for the GPU and CPU when under a medium to heavy strain. But for this build I'd guess a 650 W PSU to 750 W would be fine. I've found its best to go safe with a little more power draw than less with a pricy gaming rig.(I spent 5 years ploting my rig which if you like you can probably see in my community profile. XD.) Plus a PSU head room can give you the option to upgrade your GPU at will if you want to. 

Smelyn

Alright ty

TSTonyV

To add to what @BubbleMax said, a 650W PSU would be plenty for this kind of rig. Even a 500W would be perfectly fine. 

Personally, I'd recommend going with a power supply that's at least 80+ Bronze certified as that'll give you a good baseline for efficiency without being too pricey. If you're thinking really long term, a high-quality 80+ Gold like an EVGA Supernova or Seasonic Focus PSU should last you a very long time.