San Francisco - A power failure left much of the city without electricity yesterday, delaying outbound flights and leaving thousands of commuters stranded as subway trains ground to a halt. A problem at a power substation in San Mateo County, just north of San Francisco, is believed to have shut-down two Pacific Gas and Electric power plants at 8:17 a.m. (4 p.m. Irish time), leaving 327,000 customers without electricity.