You can lead to a lack of innovation if you only mandate one option like that. Companies will always look for the cheapest way around daft legislation, instead of pushing forwards.
USB-C is far from perfect the standard is a confusing mess TBH, also the transformer part started being mostly female type A so IMO there wasn't an "issue" with waste to begin with...
We are talking specialist parts here not consumer, you would have to aim for a standard sized PSU slot for alarm systems first and there is no way that would happen.
It would be much better to have efficiency and durability targets mandating electronics last and have free replacements for XX years and the old ones exchanged so the manufacturer dispose/recycle them.
That would remove as much disposable junk electronics from the market because if it's make cheap the manufacturer will have to foot the cost.