US trade regulators have opened a patent investigation that could block power-supply products from major Taiwanese electronics makers, bad news for Foxconn, Quanta and Delta Electronics.

• The US International Trade Commission is investigating 20 companies over vertical power delivery systems used in AI computing gear.
• The case comes from a complaint by Vicor, a Massachusetts power technology firm, which wants the products barred from the US market.
• Taiwan's Foxconn, Quanta and Delta are named along with their US and China subsidiaries, plus Luxshare, Infineon, Flex and Celestica.
• Opening a probe is not a finding of infringement — a judge will hold hearings first, and the commission sets a target completion date within 45 days.
• Meanwhile Taiwan's stock market pulled back from record highs near the 50,000 mark, with analysts calling the drop nerves rather than a turn in fundamentals.

Outlook: A judge's initial ruling is months away, so the shares at risk face a long stretch of uncertainty before any import ban could take effect.