A computer glitch caused food stamp voucher debit cards to be rejected Saturday in 17 states, leaving many unable to buy groceries. A power outage fueled the problem, causing the system to start rejecting EBT cards around 11 a.m., according to a spokesman for Xerox, who manages the system. The system was back up and running at 10 p.m., but not soon enough for many frustrated shoppers. Massachusetts supermarket cashier Eliza Shook said dozens of customers put their food back because they couldn’t afford the food. “It’s been terrible,” Shook said. “That’s what a lot of folks depend on.” The glitch was unrelated to the government shutdown, according to Xerox.