The Sidecar Power Rack: Layer 4 and the OCP-spec ecosystem
The sidecar power rack is the specific Layer 4 architecture that OCP Mt. Diablo (v0.7.0, March 2026) established as the reference for hyperscaler AI-density deployments. Physical separation of rack-level power conversion (800V DC to 48V DC) from the IT compute rack. Enables specialised thermal design, shared power across multiple IT racks, and service without IT downtime. The OCP-spec ecosystem. Wiwynn, Foxconn, Delta, Advanced Energy, plus specific power module + connector vendors. Competes intensely on this specification. This supplement covers what the sidecar rack actually does and the vendor landscape shaping the ecosystem.
- A. The Transition Tax
- B. Hybrid Forever
- C. The Voltage Ceiling
- D. The Solid-State Transformer
- E. The Sidecar Power Rack (you are here)
- F. The Connector Wars
Companion to the 13-essay main seriesStart with The Architecture Map.
- Sidecar architecture
- Physical rack adjacent to but separate from IT compute rack. Takes 800V DC input, outputs 48V DC to multiple IT racks. Enables shared power + specialised thermal + service without IT downtime.
- OCP Mt. Diablo
- Reference specification v0.7.0 (March 2026). 80+ ecosystem partners. Reference for hyperscaler AI-density deployments 2027 onward.
- Vendor ecosystem
- Rack OEMs: Wiwynn, Foxconn, Inventec, Quanta. Power modules: Delta, Advanced Energy, Lite-On, Bel Power, Flex, Murata. Connectors: TE Connectivity, Molex, Amphenol (see Supplement F).
- Competitive dynamics
- Anyone can build to OCP spec, and many do. High-competitive layer where operator procurement leverage exists.
- Cost per kW
- Sidecar architecture ~5-10% higher upfront capex vs integrated but wins on TCO through shared-power efficiency + serviceability.
- Adoption trajectory
- 2026: pilots. 2027-2028: hyperscaler default for new AI-density builds. 2029+: mainstream for mid-cap operators.
01What the sidecar power rack does
Traditional AI-DC rack architecture places 48V rectifier + PSU inside the IT compute rack itself, at the bottom. Power conversion + compute share the same physical enclosure + thermal envelope. Works fine at moderate density. At AI-density (100+ kW/rack), heat rejection from power conversion competes with heat rejection from compute for the same cooling infrastructure. Serviceability of power components requires IT downtime.
Sidecar architecture solves this by physically separating power conversion. A dedicated sidecar rack (typically 42U or similar) sits adjacent to a group of IT racks (typically 2-6 IT racks per sidecar). Sidecar takes 800V DC from building distribution, converts to 48V DC (via isolated DC-DC modules), outputs 48V to a shared busbar that feeds the multiple IT racks. Sidecar has its own thermal envelope (typically air-cooled with dedicated fans + heat exchanger). IT racks are dedicated to compute + storage + networking, thermally optimised for those loads.
02Rack-level architecture comparison
Chart 1. Rack architecture capex + TCO comparison per MW
Sidecar: $180-220k/MW upfront, $18-22k/MW annual opex. Integrated: $155-190k/MW upfront, $22-26k/MW annual. Distributed: $200-240k/MW upfront, $25-30k/MW annual. Sidecar wins TCO by year 3-4 despite higher upfront.
03The OCP Mt. Diablo spec ecosystem
OCP Mt. Diablo v0.7.0 (published March 2026) specifies the sidecar rack physical dimensions, electrical interface, cooling interface, and management protocol. 80+ ecosystem partners have committed to build to spec or integrate with spec-conforming products. This creates a specifically competitive vendor layer. Any rack OEM can build a Mt. Diablo sidecar, any power module vendor can build modules to slot in, any connector vendor can meet the interface spec. Result: procurement leverage for operators buying sidecar systems is higher than at any other layer.
Chart 2. OCP Mt. Diablo ecosystem participation 2024-2026
2024: initial working group ~15 companies. 2025: v0.6 draft with 40+ committed. 2026: v0.7.0 published with 80+ ecosystem partners committed. Growing at ~50% annually with hyperscaler-scale operator demand pulling participation.
04Vendor landscape by module type
Within the sidecar ecosystem, four distinct vendor sub-segments compete. Rack OEMs (Wiwynn, Foxconn, Inventec, Quanta) build the physical rack + integration. Power module vendors (Delta, Advanced Energy, Lite-On, Bel Power, Flex, Murata) build the 800V-to-48V conversion modules that slot into the sidecar. Connector vendors (see Supplement F). Management + BMC software vendors integrate for monitoring + control.
Chart 3. Sidecar vendor market share by sub-segment (2026)
Rack OEMs: Wiwynn ~30%, Foxconn ~25%, Inventec 15%, Quanta 15%, other 15%. Power modules: Delta ~28%, Advanced Energy 22%, Lite-On 15%, others 35%. Fragmented + competitive across all sub-segments.
05Adoption trajectory 2026-2030
Sidecar adoption tracks hyperscaler AI-density deployment cadence. 2026: hyperscaler pilot deployments (Microsoft, Meta, Google). 2027: hyperscaler production deployments for new AI-density facilities. 2028: mid-cap operators begin adoption. 2029-2030: mainstream for new construction. Legacy integrated + distributed architectures continue in existing facilities but rare for new AI-density builds by 2029.
Chart 4. Sidecar rack adoption 2026-2030 (% of new AI-density DC construction)
2026: ~15% of new AI-density DC construction. 2027: ~35%. 2028: ~55%. 2029: ~72%. 2030: ~82%. Rapid adoption driven by OCP standards clarity + hyperscaler pull + vendor supply availability.
Method and sources. Public information only. OCP Mt. Diablo v0.7.0 specification March 2026. Vendor product documentation + investor commentary 2024-2026. Industry reporting on OCP ecosystem growth.
Series footer. Supplement E to The DC-DC TransitionRelated: Supplement F (connector interface deep-dive), DC-DC X (standards evolution), DC-DC XI (vendor economics)Hub: 800V DC hub.
