Hello @x1984 and thanks for posting on the Microcenter Community Forum. The G436 already comes with a RTX 3070, so a 3090 can fit. The G436 has a 750W PSU, for a 3090 the recommended PSU is a 850w PSU. So if you get a 3090 for the G436 invest in a 850w PSU as well.
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