Some Asus ROG Strix PSUs market themselves as having GaN transistors, yes.
Of course, given that ATX power supply vendors produce a standard-sized product, and they're limited to the ~1600W that Americans can draw from their 110v sockets, the GaN products are neither smaller nor higher power (though they might run a bit cooler or more efficiently).
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Some Asus ROG Strix PSUs market themselves as having GaN transistors, yes.
Of course, given that ATX power supply vendors produce a standard-sized product, and they're limited to the ~1600W that Americans can draw from their 110v sockets, the GaN products are neither smaller nor higher power (though they might run a bit cooler or more efficiently).