The woman was found wearing headphones with burns on her chest and ears at her home in Gosford, north of Sydney, in April.
The Department of Fair Trading which assisted the probe in the case said that the charger she was using was not compliant with Australian standards, according to an ABC report.
Police have defended the two-month delay in releasing the information about the case.
"We moved as quickly as we can. I understand initially there was not clear information about the cause of the fatality," Fair Trading Commissioner Rod Stowe was quoted as saying in the report.
The department warned consumers about the dangers of sub-standard devices and asked them no to use them while they are plugged in to a power source.
"These devices pose a serious risk of electrocution or fire," Stowe said.
"Fair Trading has detected a large number of these [chargers], along with travel adapters and other power boards, at a store in Campsie and these have been removed from sale," he said.
The USB's seller based in Campsie, in Sydney's south-west, was now being questioned by police and couldface charges.
Maximum penalties for a person selling devices that fail Australian standards are AUD 87,500 and/or two years imprisonment and for a corporation the fine is AUD 875,000.