PC Keeps Shutting Down During Gaming – Need Help!

Hey everyone, I'm really stuck on an issue with my PC and could use some guidance. Here are my specs:

- **CPU:** AMD Ryzen 5 5600X
- **GPU:** Gigabyte Radeon RX 6650 XT
- **Motherboard:** MSI MAG B550 Mortar Max WiFi
- **RAM:** 4x8GB (2 sticks of DDR4-3200 and 2 of DDR4-2400) from Patriot
- **SSD:** WD SN570 250GB (for boot) + 1TB (storage)
- **Original PSU:** Chieftec Task TPS-700S (700W Bronze)
- **Current PSU:** Thermaltake GF 750W Gold
- **Case:** Ginzzu CL220
- **CPU Cooler:** ID-Cooling SE-224-XTS ARGB WHITE
- **OS:** Downgraded from Windows 11 to Windows 10 (no improvements)

I've been facing these issues ever since I built the PC two years ago. It shuts down instantly while playing games, kind of like the power just gets pulled. No blue screens or warnings, just sudden power loss. In most games like *Baldur's Gate 3* or *Space Marine 2*, it happens at random—sometimes after 10 minutes, sometimes 2 hours. Recently, it has started crashing consistently within 5 minutes of playing *Clair Obscur: Expedition 33*, making it unplayable. I've also had a shutdown when generating images with Stable Diffusion.

So far I've:
- Replaced the PSU (no difference)
- Passed stress tests (Prime95, FurMark, etc.)
- Monitored temps (CPU below 89°C, GPU below 55°C under load)
- Logged power with HWiNFO64 (steady +12V and +5V)
- Set GPU power limit to -6% (no change)
- Updated BIOS (no improvement)
- Tried downgrading Windows (11 to 10) and it didn't help.

Symptoms include:
- Instant shutdowns (no warning)
- Event Viewer shows generic unexpected shutdown (Event ID 6008)
- Fans ramping up before crashes (not sure which ones)
- Only crashes during GPU-heavy tasks, never during CPU-only workloads.

I'm hopeful someone can help me troubleshoot this issue—I'm ready to dive into any possibility!