TBH it's probably more a case of me not catching up on all of what has been written and just skim reading. Turns out the debate is fairly pointless. The full technical guide can be viewed here: https://www.dell.com/learn/us/en/04/shared-content~data-sheets~en/documents~optiplex-790-tech-guide.pdf 17A on the 12V rail. Two users reporting typical peak power draw with a 1050Ti as ~180W, and sustained power draw (when gaming) at ~130W here: http://www.tomshardware.co.uk/answers/id-3271557/gtx-1050-dell-optiplex-790-sff.html The technical guide shows 90%-87% efficiency at 50%-100% load. So 180W AC would be ~162W DC supplied by the PSU. Subtract the power draw on the 3.3V and 5V rails, and that should leave something in the region of 150W on the 12V. So roughly ~50W spare (±5W) at peak measured draw (i.e. running benchmarks). Typical use (gaming) leaves closer to 100W spare. So it's a question of risk; do you trust a £100-£150 GPU to an 8 year old Dell PSU? For a little over £200, it's not a bad gaming PC...
The chart you would need for the point I have been making is the temperature under load for differing PSU efficiencies. Outside OEM the active thermal management is to a far higher standard and as I have already stated in OEM what is defined by what max wattage means has no real defined standard. Your chart show at the edges of the output that is when least efficient. At the bottom edge 50 percent of not a lot is not a great amount of heat to dissipate. At the top edge and under load a high percentage of which makes the significant amount. Heat to lifespan expectancy to a psu then there is this chart and the correlation I am talking about: Which is my point - running over the spec Dell have specified will produce more heat moving you to the right on this chart which in turn has a direct relationship on the estimated lifespan of the unit. Other than that I am not disagreeing on pretty much most the other points made. This isn't rocket science in its concept although perhaps I am doing a really bad job in making my point clear.
I’m not saying it’s pleasant on 1-2GB but it’ll be fine with 4GB, though at £30 more to get to 8GB RAM and a 120GB SSD you’d be mad not to. Quad-core Core i5/7 any generation is still fine even today, you can thank AMD for producing rubbish until Ryzen appeared ensuring Intel didn’t need to do anything other than minor clockspeed increases, fractional efficiency gains and iGPU improvements.
Except this is no high end gaming PC. Buy it for the kids whack in a GT1030, keep the resolution at 1080p and your good for Fortnite all day long. Alternately use the same graphics card and you've got a great 4K HTPC machine. No over stressing PSU's and no excess heat...Job done. Now the kids are playing on the Dell you can finally claim back your main computer... :D .
It's an old article, but this one pretty much settles the debate: https://www.anandtech.com/show/2624/debunking-power-supply-myths Their example 900W PSU is most efficient when power draw is between 400W and 700W. It's a similar story with the other PSUs they tested; best efficiency falls in the range of 45%-75% maximum load.