My personal opinion is that there is no need to go for anything different than Seasonic unless you're budget shopping or have peculiar need for warranty ( like US region where warranty is otherwise limited).
Corsair, BeQuite, EVGA and other reputable brands source their PSU from various OEMs like Seasonic, Super Flower, Channel Well,etc.
So particular Corsair AX can be made by Seasonic, but AXi by Flextronics & Chicony.
And seriously, do you want Seasonic or Chicony to manufacture your high-end 200+ Euro PSU ? Just get Seasonic.
There is hardly anything better than Seasonic Prime models (G/P/T) on the market right now, it's the latest&greatest. Unparalleled build quality, look at any review.
The only tiny critique I have ever seen on Prime could be sometimes more aggressive fan curve, but this isn't going to be an issue if you go over 1k watt (and you should do that for 2990WX + 1 or 2 GPUs) and I personally find it still super silent.
I have used Prime Titanium for file server and Prime Gold for past two workstations I've build. Will also use Prime Gold 1200W this time.