Just been looking at this, and volume wise none of these new GaN chargers are significantly more dense than a 500w flex PSU. Perhaps more efficient? Less Heat?
The Silverstone 500w flex is 1010W/L
The SlimQ linked is 904W/L
The 'ThunderGo' (afaik, the smallest 200w 'GaN charger') is 1119W/L...