

I don’t think a Platinum vs a Gold ATX rated PSU is going to make such a drastic difference on such low wattages, unless they’re made for low workloads. Efficiency is highest around half of the rated maximum load.
So something like a PicoPSU is likely more efficient, and if electricity is very expensive you could even make a return on that investment in 5-10years maybe…I wouldn’t worry too much about a 5-10W difference (unless the pc will be off-grid), at the same time a quality PSU will produce less heat and be more silent, will have a fanless mode built in, those are bigger advantages to me.
Keep using the Superflower my friend, and keep the Pico + Dell transformer as backup if the first fails. Maybe in a year or two you’ll find a great deal on a mobo+cpu combo that’s way more efficient and powerful anyway so all investments made now for a few watts will seem moot by then. Just my 2c.
Btw I also have an old Superflower but only 350W, and I recently got a used (barely) Seasonic Focus 550W in case I needed more wattage again (for multiple HDDs spinning up at boot or in case I bought a GPU again), also gold-rated. I was looking to get a Titanium or Platinum one but the price difference was still quite unjustifiable for my use case (idle server/NAS).
Another thing, I never bothered testing with a wattmeter (except the one on the UPS display) because I read that they’re a lot less accurate at the low wattages that we are discussing. Also the UPS alone causes some losses as well.