By Aditya Soni

April 30 (Reuters) - Super Micro Computer SMCI.O shares tumbled 15% before the bell on Wednesday after the server maker slashed its revenue forecast, the latest blow to the former AI darling trying to regain investor confidence following late filings and short-seller attacks.

The company blamed the cut on delays in purchases from customers, fanning worries that big technology companies were reining in spending on AI infrastructure as the economic outlook worsens and the short-term returns remain uncertain.

While several Big Tech firms have reaffirmed their hefty AI spending plans in recent months, analysts say Microsoft MSFT.O and Amazon.com AMZN.O have slowed new data center leases as they become cautious about expanding capacity.

But several analysts including those at brokerage J.P. Morgan said Super Micro's cut was unlikely to be representative of any industry-wide slowdown in demand or supply constraints.

This was "driven by specific customer decisions on platforms which shifted in relation to timing," J.P. Morgan analysts said, while Rosenblatt Securities called them "isolated issues".

While Super Micro, seen as a proxy for Nvidia demand, fell sharply, Nvidia NVDA.O itself slipped just 1.5% in premarket trading and Advanced Micro Devices AMD.O fell 0.7% - small declines that signaled investors may be shrugging off the warning. AI server rivals Dell DELL.N and Hewlett Packard Enterprise HPE.N slid 2.8% and 0.7%, respectively.

Some analysts said the cut could deepen investor scrutiny of Super Micro's forecasts, given it had predicted just last month that sales would be around $40 billion in its next fiscal year, almost twice what analysts expect for the current one.

With its shares soaring more than triple in value in 2023, the company was one of the biggest winners of the generative AI boom until last year when it had to delay its annual report, lost its auditor and faced short-seller reports from the now-disbanded Hindenburg Research. Last year, its stock rose 7.2%, widely underperforming the benchmark S&P 500 index .SPX

(Reporting by Aditya Soni in Bengaluru; Editing by Krishna Chandra Eluri)

((Aditya.Soni@thomsonreuters.com; +91 80 6210 0555;))