Pragmatically, even if you manage to reduce power consumption by 45W you'd only be saving 1kWh per day. That's $0.11/day (depending on your local power costs, of course; I'm using $0.11/kWh).

Your yearly saving using such a device would be $40. A 'wall-to-dc converter' designed for a ~600W load would cost many times more than that. Sales volume would be low, since it would have little or no use beyond this niche application; so amortizing the non-recoverable engineering costs to design it would bump the per-unit price even further. Not to mention the expense of UL/CE certification that would be required.

Such a product would be unlikely to ever pay for itself.