Bay of Plenty consumers' electricity bills have jumped by up to $175 over the past year.
The increase is being blamed on grid maintenance costs but has sparked warnings about the ability of poor families or those on fixed incomes to pay.
Tauranga lines provider Powerco increased its electricity distribution charges, including transmission charges, by an average of 9 per cent from April 2012 this year, pricing manager Michael Warren said.
"This equates to an increase of around $5 per month for the average residential customer."
Figures from the Ministry of Business, Innovation and Employment (MBIE) showed average power bills in Tauranga increased $75 in the 12 months to August.
The same report showed Energy Online raised its charges $178 for the same period.
Mr Warren said the price increase was due to a significant increase in Transpower's charges to Powerco - reflecting the amount of investment in critical infrastructure.
"Retailers then determined how and when they passed these costs on to their customers," he said.
Powerco's distribution charges make up on average 35 per cent of the overall costs retailers pass on to customers, Mr Warren said.
An Energy Online spokeswoman said that, based on information on Powerswitch, Energy Online's pricing was among the most competitive in the Bay of Plenty.
"Energy Online did increase their charges during the last year but this was the first increase since April 2010," she said.
MBIE figures showed power bills nationwide have risen by up to $358 in the year to August.
The ministry found New Zealand's two million power consumers faced an average 5.4 per cent increase in their bills in the last year.
Electricity Authority chief executive Carl Hansen said the Government's What's My Number campaign was launched to promote greater competition in the retail electricity market.
"Barring a major gas find or technology breakthrough, retail electricity prices are likely to continue to rise as demand increases over the next few decades," he said. "That is simply the reality of a natural-resource-based industry, where generators tap the cheapest resources first and then the next cheapest and so on over time.
"However, promoting competition can and has made a difference."
There were 885,659 visitors to the What's My Number website from June to August, resulting in 490,117 households switching power companies.
An international survey this month found New Zealand had the second-highest rate of consumers switching power companies - saving almost $9 million collectively.
VaasaETT, an energy think-tank in Finland, found that almost a fifth - 19.5 per cent - of New Zealand consumers switched power companies last year, up from 10.5 per cent in 2008.
Increased competition and consumer switching had been credited with electricity prices dropping in 2011, Mr Hansen said.
However, power prices have since increased - stemming from line charges increases.
Nationally, the biggest average increase for the year to August was Pulse Energy's $358 for its Nelson consumers using Marlborough lines.
At the other end of the scale, bills for TrustPower customers on Network Waitaki lines in Otago fell by $201.
New Zealand Federation of Family Budgeting Services chief executive Raewyn Fox said rising electricity costs were making it harder for poor families to get by or put food on the table.
"One thing we do find is that the lower-income families for whom things are really, really tight tend to have older power appliances that are less power efficient," she said. The lower a family's income, the higher their power usage tended to be, Ms Fox said.
"They can't afford to fix the seals around their fridge and stove and they have really old heaters that chew through the electricity."