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desktop tower: install Corsair RM850x 2024 PSU #84

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opened 2026-05-23 20:54:39 +00:00 by coilysiren · 1 comment
coilysiren commented 2026-05-23 20:54:39 +00:00
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Originally filed by @coilysiren on 2026-04-29T01:29:25Z - https://github.com/coilysiren/infrastructure/issues/76

🤖 Filed by Claude Code on Kai's behalf.

Goal

Replace the desktop tower's existing PSU with a Corsair RM850x (2024). Hard dependency for #75 - the RTX 3090 draws 350-400W and the existing PSU is sized for the RTX 2080 (~225W) and almost certainly undersized for what's coming.

Part

Corsair RM850x (2024), model CP-9020270-NA, ASIN B0DJ1JL3MK. Amazon link.

  • 850W, 80+ Gold / Cybenetics Gold certified
  • ATX 3.1 compliant, native 12V-2x6 connector (future-proofs for any 4090/5090 upgrade in this PSU's 10-year lifetime)
  • Fully modular cabling
  • Japanese capacitors, low-noise fan with zero-RPM mode
  • 10-year warranty
  • Typical price $140-150, MSRP $169.99, occasionally drops to $124.99 on Slickdeals

Why this PSU

  • 850W is the right size for an RTX 3090 single-GPU build with an i7-8700. 750W can technically run a 3090 but the 3090's transient spikes (up to 500W under load) eat headroom fast.
  • Corsair RMx line has a long track record. The 2024 refresh added ATX 3.1 / native 12V-2x6 without raising the price meaningfully.
  • Alternatives considered: Seasonic Focus GX-850 V4 (similar tier, slightly noisier under load, get if $20+ cheaper on the day), Corsair RM1000x (only worth the +$30-40 if seriously planning a 4090/5090 future).

Install plan

PSU swap and GPU swap should happen in the same session - opening the case once, fully recabling, single test boot.

  1. Order RM850x ahead of the GPU; receive and stage in the box.
  2. When the 3090 arrives:
    1. Power down, unplug from wall, hold power button to discharge.
    2. Disconnect every cable from the existing PSU. Note which modular cables go where on the new PSU before discarding the old ones - modular PSU cables are NOT cross-compatible between brands or even between Corsair generations.
    3. Unscrew old PSU from case, remove.
    4. Install RM850x, run cables: 24-pin ATX, 8-pin EPS (CPU), 3x PCIe 8-pin to GPU (FTW3) or 1x 12-pin native to GPU (FE), SATA power for the 2.5" SSDs.
    5. Cable management before closing the case.
  3. First boot, listen for fan spin-up, confirm POST.
  4. Boot Windows, confirm clean.

Acceptance

  • PSU arrives, stages in the box.
  • Old PSU removed.
  • RM850x installed, all cables routed.
  • System POSTs and Windows boots cleanly.
  • Power draw under load looks sane (HWInfo / GPU-Z reads ~225W idle, peaks correctly under load once 3090 is in).
  • desktop-tower.md PSU section updated with the new part.
  • Old PSU set aside for resale, donation, or e-waste depending on age and condition.

Related

  • refs #75 (RTX 3090 swap) - this is the gating dependency. Land PSU first, then GPU.
  • refs #74 (NVMe SSD) - SSD install can happen in the same case-open session if convenient, but doesn't require this PSU.
  • refs #73 (evaluate self-hosted models on desktop tower) - root motivator.

🤖 Filed by Claude Code on Kai's behalf.

_Originally filed by @coilysiren on 2026-04-29T01:29:25Z - [https://github.com/coilysiren/infrastructure/issues/76](https://github.com/coilysiren/infrastructure/issues/76)_ > 🤖 Filed by Claude Code on Kai's behalf. ## Goal Replace the desktop tower's existing PSU with a Corsair RM850x (2024). Hard dependency for #75 - the RTX 3090 draws 350-400W and the existing PSU is sized for the RTX 2080 (~225W) and almost certainly undersized for what's coming. ## Part **Corsair RM850x (2024)**, model `CP-9020270-NA`, ASIN `B0DJ1JL3MK`. [Amazon link](https://www.amazon.com/dp/B0DJ1JL3MK). - 850W, 80+ Gold / Cybenetics Gold certified - ATX 3.1 compliant, native 12V-2x6 connector (future-proofs for any 4090/5090 upgrade in this PSU's 10-year lifetime) - Fully modular cabling - Japanese capacitors, low-noise fan with zero-RPM mode - 10-year warranty - Typical price $140-150, MSRP $169.99, occasionally drops to $124.99 on Slickdeals ## Why this PSU - 850W is the right size for an RTX 3090 single-GPU build with an i7-8700. 750W can technically run a 3090 but the 3090's transient spikes (up to 500W under load) eat headroom fast. - Corsair RMx line has a long track record. The 2024 refresh added ATX 3.1 / native 12V-2x6 without raising the price meaningfully. - Alternatives considered: Seasonic Focus GX-850 V4 (similar tier, slightly noisier under load, get if $20+ cheaper on the day), Corsair RM1000x (only worth the +$30-40 if seriously planning a 4090/5090 future). ## Install plan PSU swap and GPU swap should happen in the same session - opening the case once, fully recabling, single test boot. 1. Order RM850x ahead of the GPU; receive and stage in the box. 2. When the 3090 arrives: 1. Power down, unplug from wall, hold power button to discharge. 2. Disconnect every cable from the existing PSU. Note which modular cables go where on the *new* PSU before discarding the old ones - modular PSU cables are NOT cross-compatible between brands or even between Corsair generations. 3. Unscrew old PSU from case, remove. 4. Install RM850x, run cables: 24-pin ATX, 8-pin EPS (CPU), 3x PCIe 8-pin to GPU (FTW3) or 1x 12-pin native to GPU (FE), SATA power for the 2.5" SSDs. 5. Cable management before closing the case. 3. First boot, listen for fan spin-up, confirm POST. 4. Boot Windows, confirm clean. ## Acceptance - [ ] PSU arrives, stages in the box. - [ ] Old PSU removed. - [ ] RM850x installed, all cables routed. - [ ] System POSTs and Windows boots cleanly. - [ ] Power draw under load looks sane (HWInfo / GPU-Z reads ~225W idle, peaks correctly under load once 3090 is in). - [ ] `desktop-tower.md` PSU section updated with the new part. - [ ] Old PSU set aside for resale, donation, or e-waste depending on age and condition. ## Related - refs #75 (RTX 3090 swap) - this is the gating dependency. Land PSU first, then GPU. - refs #74 (NVMe SSD) - SSD install can happen in the same case-open session if convenient, but doesn't require this PSU. - refs #73 (evaluate self-hosted models on desktop tower) - root motivator. > 🤖 Filed by Claude Code on Kai's behalf.
coilysiren commented 2026-05-30 05:43:28 +00:00
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Iceboxed in the 2026-05-29 backlog burn-down: buy/install PSU hardware toy. Reopen anytime if it becomes real.

Iceboxed in the 2026-05-29 backlog burn-down: buy/install PSU hardware toy. Reopen anytime if it becomes real.
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