How about Super Flower and their Leadex series? In my nick of the woods, Super Flower is the one that is really hard to find, while Seasonic is common.
There are more nuances what ATX 3.0 PSU standard brought, over previous ATX 2.5 standard. Seasonic has made a nice explanatory article about it,
article:
https://seasonic.com/atx-3-0-standard
But most prominent feature is, that this adapter cable:
Is replaced with this direct cable:
At the end of that cable is the new +12VHPWR connector, that is in use with RTX 40-series GPUs.
When RTX 30-series launched, Nvidia made new power connector for GPUs, that can sustain higher wattage capacity than the regular 6-pin PCI-E (75W) and 8-pin PCI-E (150W). That connector was known as 12-pin PCI-E. Required adapters were included with each RTX 30-series GPU, where connector on one end, was 2x 8-pin PCI-E and on the other end, the new 12-pin PCI-E.
With RTX 40-series launch, Nvidia fine-tuned the new 12-pin PCI-E cable, adding additional 4 small pins (mostly "Sense" pins), making the connector essentially 16-pin PCI-E, what Nvidia called as +12VHPWR (+12 Volt High PoWeR) and with a rating of up to 600W, to be able to power RTX 4090. At first, another adapter was included with each GPU, and depending on a GPU, there were 3 different adapters;
1. 2x 8-pin PCI-E to +12VHWPR - 300W rating (used for up to RTX 4070)
2. 3x 8-pin PCI-E to +12VHWPR - 450W rating (used for up to RTX 4080)
3. 4x 8-pin PCI-E to +12VHWPR - 600W rating (used for up to RTX 4090) (1st image i linked)
To get rid of that adapter (since many of them melt when using RTX 4090), ATX PSU standard revised their specs for PSUs, and one such change was direct cable from PSU to +12VHPWR connector with a rating of 600W (2nd image i linked).
Another major change was that ATX 3.0 PSU has to be able to sustain twice the rated capacity for certain amount of time. This is to combat GPU transient power spikes.
And there are other changes too, that you can read form Seasonic article.
Currently unknown, but it is possible that Nvidia keeps the new +12VHPWR connector in use for their upcoming RTX 50-series GPUs (and possibly for all other upcoming GPU series as well). Though, AMD still uses the standard PCI-E 6-pin and 8-pin connectors on their GPUs, since +12VHPWR connector is Nvidia thing. Only time will tell if AMD also starts using the +12VHPWR connector on their Radeon GPUs or not. Or they develop their own, proprietary power connector for GPUs.