This is verifiable in manufactures data sheets.

Efficiency at less than 20% and greater than 80% loads isn’t great relative to in between those ends.

This is compounded by lower wattage PSUs being more limited with regard to features and benefits.

If you end up with a 650w PSU and your system idles at 80 watts for the bulk of a working day you spend long periods of time in this less efficient window.

We need to see some quality 300w to 600w designs come back onto the market.