There's basically no point. Desktop PSU is a solved problem, most designs are all about cost engineering and the tiny sliver of higher power and ultra high efficiency options are not struggling with their current form factor.

In the data center, where power (and cooling) are the only significant OpEx, GaN point-of-load conversion is everywhere. Common as a rack distributed 48V to 12V bus or direct to processor Vdd (2% duty cycle is feasible with GaN thanks to fast on/off times). There was a while where GaN was used as part of the power factor correction for AC to DC in the server power supply, back when passing 400VAC or 800VAC bus around made sense. I think these days it's mostly back to DC buses, and AC-to-DC is all happening farther back, in part because of widespread solar deployments and trying to avoid DC->AC->DC double conversion losses when possible. So maybe GaN gets use on active secondary rectifier in the bus -> 48V now too.

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).