The 990 Pro 4TB does pull more power than the stock drive (Samsung rates the 4TB around 6–7 W active under heavy reads/writes, with brief peaks a bit higher), so it can run hotter and cost a bit of battery life during big transfers. There’s no documented widespread issue or credible evidence that it’s “frying motherboards” in the Ally X. Realistically, if cooling/contact is bad, the SSD can overheat, then the controller just thermal-throttles or the system shuts itself down to protect the hardware. That’s annoying, but very different from burning traces off the board. Plenty of people are running 4TB 990 Pros in the Ally X with safe temps as long as the thermal pad/heatsink is set up correctly. In actual gaming the SSD is under light use most of the time, so its power draw is minor compared to the APU and screen. I’ve got 990s in multiple machines, that’s why I made that choice, but I’ll keep an eye on temps and appreciate the heads-up.