Another option....
I wholeheartedly agree that you should RMA your AX1200i to Corsair, and request an advanced RMA, so that you're not without a PSU in the interim.
But if you're determined to purchase a new PSU anyway, may I suggest that you buy their platinum efficiency equivalent HX1500i. NewEgg is currently selling it for $400 plus a $50 instant promo code. The 1,000 watt version is only $260.
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CORSAIR HX1500i Platinum Certified Full Modular Power Supply
$399.99 (+ $50 off w/ promo code CSMAYD6, limited offer)
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CORSAIR HX1000i Platinum Certified Full Modular Power Supply
$259.99
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Btw, the Corsair HX1000i / HX1500i / AX1600i weigh 4.39 / 5.28 / 12.80 pounds respectively. As someone who owns the competitor to the AX, EVGA T2 1600, I personally wouldn't want to add that much weight (and girth) to a rig unless I really needed it. Just my opinion.
Addendum: If you're willing to consider Super Flower and their EVGA counterpart, the options below are also very good. The Super flower models below are used almost exclusively in Puget Systems custom builds. Again, I'll mention that the EVGA T2 1600 below is as heavy as the Corsair AX1600i, almost 13 pounds, plus the weight of the cables themselves. Both are lengthy units as well. The SeaSonic Vertex has the
new ATX 3.0 / PCIe 5.0 compliant 16 pin connector, which your RTX 3090 Ti could connect to with a singular power cable, instead of three cables into the adapter.
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Super Flower Leadex Platinum SE 1200W 80+ Platinum, 10 Years Warranty
$209.99
www.newegg.com
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Super Flower Leadex Platinum 1600W 80+ Platinum, 10 Years Warranty
$309.99 (+ $40 off w/ promo code MYRSSCS977, limited offer By Super Flower)
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EVGA SuperNOVA 1600 T2 220-T2-1600-X1 80+ Titanium
$359.99
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Seasonic VERTEX GX-1200, 1200W 80+ Gold, ATX 3.0 / PCIe 5.0 Compliant
$289.99
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