Whilst you should dump some power with a resistor in series with each string, switching the strings on and off quickly is the most efficient way to control brightness.

Unless you use an inductor in series with the LEDs to control the current, PWM is no more efficient than linear current control.

 

LED's can be "overdriven" with a PWM signal as long as the average power doesn't lead to thermal runaway. .

The nature of the PWM has to be an exponential curve as LED's are non-linear in nature.

 

That is why no one builds mains transformer power supplies any more. For less money than the transformer, you can buy a good commercial switching supply.

For example

They still do, just not for cheap consumer products.
https://www.acopian.com/linear-power-supplies.html
https://www.acopian.com/linear-powe...power-supply-vs-unregulated-power-supply.html

 

This guy makes custom supplies, also manuf./winds Toroidal transformers.
https://www.antekinc.com/power-supplies/

 

The 1074 Switcher that I suggested has an "Enable" Input that
can be used for relatively low-Frequency PWM Dimming. ( ~200hz )
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