Frankly, the whole 'new PSU' idea is a mess. Even if you somehow jerry rig everything, there is no guarantee that your motherboard uses standard power connectors. These PC's are made by Dell for office use mostly, and they've customized these PC's to the point where if you want to change even one little thing you'll literally have to change half the PC with it.
Take for example, the PSU upgrade you're looking for. For this, you'll firstly need a new case for the PSU to fit. Then, the Dell motherboards are not standard sized, so you'll need a new motherboard because the Dell one won't install in your new case. Chances are that the CPU cooler is also custom, so you'll need a new CPU cooler to go with your new motherboard. And then you can buy a new PSU and install it.
As I've been hinting for this whole thread, just drop the idea of a GPU upgrade IMO. either that, or just risk it a little bit and use the GTX 1050 with your current PSU, which I do NOT recommend doing unless you're fine with the whole PC going bad in the near future/immediately.