Does the Dell XPS 8950 have the same power supply issue as the previous model?

Yes, the XPS 8950 keeps the same PSU quirk as the 8940 — a standard ATX PSU body but with a proprietary motherboard connector. You can upgrade to a bigger power supply, but you’ll need a pinout adapter. It’s a mild annoyance, but still far better than a fully soldered or proprietary-only PSU.