I'd get the 850 and be done with it, the 2060 requires 500w minimum according to Newegg. Just checked your build and think you can add 850w and liquid cooling for $150, that's what I'd select, you'd be quite happy with that setup.

I can't comment specifically on the 2060, but most of the video cards used are OEM versions and tend to not require the amount of power the full retail version uses.  Thus what configures is usually correct.

So you think that with that 460W Psu I can have problems or just I can't upgrade my pc in the future? 

Ok but I cannot be sure about that. Do you think that I can go with that Psu without problems? 

Even if the 460W PSU suffices for your current configuration, choosing that would essentially lock you out of potential upgrades down the road.  You'd end up spending more money replacing the power supply with something more capable in future. 

When it comes to power supplies, I've always advocated buying as much as you can afford now that would give sufficient headroom for expansion when needed. 

are the OEM Video card Dell uses like the single fan 2060 RTX a Good card or does it underperform then the retail card 

It's a simple blower style card. Gets the job done but don't expect Strix/ Aorus/ FTW3 levels of performance here. You'd probably want to shelf the idea of overclocking it too much. Not sure how much the power limit is set in the vBIOS.

Even retail cards have at least 3-5 tiers of performance for each brand and RTX chip. Are you looking to be ranked top N in 3Dmark/ Heaven benchmark or just don't want a lemon flagged in Userbenchmark?

Get the Power supply now and be done with it.  You will usually need a Dell replacement to make it work in a Dell/AW box.