Power One

(PWER)

was down 27% in preopen

Island

trading after it cut revenue and earnings guidance for the year due to the slowdown at some of its largest customers, chiefly

Cisco

(CSCO) - Get Report

.

Power One, which makes power conversion devices, said first-quarter results will be close to current expectations, but the rest of the year looks doubtful.

The company also said it would speed up its cost-reduction efforts, including moving jobs out of North America and Europe.