Cummins told investors on its August call that its power-generation growth target of 15% to 25% is limited by how many engines it can build, not by how many customers want them. The company is adding 20 gigawatts of incremental global capacity phased across 2027 to 2030, and is currently taking orders for its largest 95-litre generator sets through the second half of 2028. That is a supplier rationing output — an unusual position for a diesel-engine maker whose share price is normally set by North American trucking.

The engine maker's mix is changing faster than its cycle

Cummins builds diesel and natural-gas engines, powertrains and components for trucks, construction and marine customers, and through its Power Systems segment the standby and prime-power generators that sit outside data-center campuses. Power Systems is now roughly a quarter of group revenue and it grew fastest: revenue of $2.3bn in the June quarter, up 19%, at a 24.5% EBITDA margin, 170 basis points better than a year earlier. Engine grew 6%, Components 7%, Distribution 9%. In China, power generation revenue nearly doubled on data-center construction. The truck business, meanwhile, is merely steady — the company's North American heavy-duty forecast is 240,000 to 250,000 units in a market it expects down 4%.

Group revenue was a record $9.46bn and full-year guidance was raised for the second time this year, to 10–13% growth. The stock fell 2% that day. Cummins is a clear second to Caterpillar in data-center generators, ahead of Rolls-Royce mtu and Mitsubishi, and is expanding its Fridley, Minnesota plant to shorten 18-month lead times. At 19.8x forward earnings against 29.9x trailing, the market is discounting roughly 30% earnings growth already; price to trailing gross profit is 9.2x, against 10.3x three months ago. The bear case is not demand but the supply response — David Giroux of T. Rowe Price argued at Barron's midyear roundtable that the capacity Caterpillar and Cummins are adding will erode the economics of 2030 data-center power.

Fluence has the orders and not the factory

Fluence integrates grid-scale battery storage systems, a business spun out of a Siemens and AES joint venture, and it is the one genuine break here. June-quarter revenue rose 7.9% to $649.8m, missing consensus by roughly 29%, while gross margin collapsed to 5.1% from 14.8% and gross profit fell 62.7%. The cause is manufacturing: a 15 GWh automated facility in Houston slipped a quarter on construction and equipment problems, and an international line needed rework. Full-year revenue guidance went to about $3.0bn and EBITDA to a loss.

The order book says the demand is real. Intake tripled to $1.44bn, including a first $850m of data-center awards, and backlog reached a record $6.4bn. But Fluence is a $2.1bn company that may need $300m to $500m of extra working capital next year against $863m of liquidity, and it now ranks fourth among global storage integrators behind Sungrow, Tesla and CATL. Its worst session was its own results day.

Cummins' losses arrived on somebody else's news

Four sessions account for more than Cummins' entire monthly decline; across the other seventeen the stock rose. On 29 July, Baird downgraded Caterpillar on local opposition to data-center construction — 75 projects worth about $130bn delayed or blocked in one quarter — and Cummins fell 5.5% alongside it. On 18 August the 30-year Treasury yield hit 5.337%, its highest since 2007, and everything that finances a data center repriced.

That is not a generic equipment de-rating. Generac, the standby-generator maker, booked more than $100m of data-center revenue in the quarter and guides to nearly $450m for the year, and it fell less than 4%; Plug Power, which has no data-center revenue, was flat. The names with the most AI content fell hardest.

Bloom Energy, which sells solid-oxide fuel cells that energize a data hall without waiting for a utility interconnection, sits in the middle. Revenue grew 166% to a first $1.065bn quarter and gross margin widened to 33.4%. Its price to trailing gross profit was about 129x in May and is 61x now — a full round trip to where it stood six months ago, achieved partly by a 23% rise in the diluted share count over two quarters.

The setup

Where it stands — Cummins' generator business is capacity-constrained into 2028 while its shares de-rated on rates and a rival's downgrade. Would confirm — Power Systems revenue growth holding at or above 15% in the September quarter with EBITDA margin above 24%. Would invalidate — A cut to the 15–25% power-generation growth guide, or hyperscaler order deferrals disclosed on the next call. Watch next — Cummins' third-quarter results in early November; Fluence's fiscal fourth quarter and Houston start-up in late November. Valuation — Cummins at 19.8x forward and 29.9x trailing earnings; 9.2x trailing gross profit versus 10.3x three months ago.