My PSU is failing? Unexpected instant crashes when playing games

My specs:

• RX 7800 XT
• Ryzen 7500F
• 32GB RAM (Memtested less than a month ago)
• Seasonic X series 650W (high end PSU from around 10 years ago)

I'm currently running fedora rawhide linux, but I had the same issue on Bluefin Linux Stable and Debian Sid.

When I'm starting to play a demanding game, my system crashes within 5 seconds of loading the level. I wasn't able to reproduce that with stress tests. There's nothing in the logs, they just stop.

I think that's all. I can provide more details. If you can give me meaningful troubleshooting steps, I'm willing to install another system, even windows.

In my opinion the issue is clear, the PSU is old and can't keep up with the GPU, so I should probably replace it.

I don't want to do that, so if you have any other idea, please let me know.

What specs should I aim for for the new PSU?

Edit: I'm cooked, I tried booting the PC to make some tests again, but I'm getting a red motherboard light for CPU. The PC boots tho

Edit2: I found those deals on PSUs. I live in Poland, so prices are at least 25% higher than in the US:

• Corsair RM850e 2025 for $110
• FSP VITA GB 750W for $82
• MSI MAG A750GL for $95