At least in theory (going off marketing materials¹ for one such device, though I personally lack first-hand experience here, and said device doesn't advertise itself as Mac-compatible), the eGPU should function as the power source for the laptop, so you'd only need one power adapter (for the eGPU).

Really, this experience actually sounds pretty pleasant.

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¹: https://www.asus.com/Graphics-Cards-Accessories/ROG-XG-STATI...