i even told him about you and he insisted that it was good, even with the 3060.
If he convinces you to keep the CX-550m and if he knows anything about PSUs, then this could be very clever way to ensure that you will return to him, again. Once CX-550m blows your new GPU as well, you're back at him to diagnose the issue. Since he is in a business, generating revenue is #1 priority. Now, if PC repair shops would fix consumer PCs following the highest standard, every client's PC would last for years, problem free. But that means loosing customers and without income, business would go bust. But if you have a client who's PC is "iffy", business can "milk" the client quite a while, or for a big sum of money (e.g PSU blows entire PC and they replace the whole thing for you).
I, in the other hand, have 0 monetary gain in helping you (or anyone else in TH forums in that matter). Only thing i get helping you, is good feeling and on a wider scope, improving TH forum's reputation as getting good PC advice. Also, there is a reason why i have "Ambassador" title in TH forums and why i'm not a regular user.
On similar example:
Let's say you have cheap tires on your car, and you slid off the road, into the ditch, while also bending two rims of your car. Now, you can't drive any further with bent rims and you go out and buy new rims. Better ones, more expensive but also better looking. Question here is: would you still put those cheap tires under your car, that caused you to bent your previous rims? Even when mechanic in the tire shop says that the tires are "good"?
Oh, tires on a car is essentially as PSU in PC. Since when it comes to the cars, tires are the only thing that touch the ground, hence why never to cheap out on car tires either.
For 1080p, GTX 1660, 1660 Super or 1660 Ti would've sufficed as well. Given that the price is cheaper than RTX 3060.
(In my main build, Skylake, full specs with pics in my sig, i'm running GTX 1660 Ti with 24" 144hz monitor and i'm getting easy 144 FPS @ 1080p, depending on a game.)
Oh, with RTX 3060, you will have transient power spikes, where GPU will consume far more power than it is rated for. Steve, from GamersNexus made a good video about it;
View: https://www.youtube.com/watch?v=wnRyyCsuHFQ
Your previous GPU, RX 5500, was 130W GPU. RTX 3060 is 170W GPU and when factoring in transient power spikes as well, RTX 3060 will push your CX-550m far harder than your RX 5500 ever was able. This is something else to keep in mind.
With RTX 3060, minimum PSU max wattage, i'd be comfortable, would be 650W range.