Utilities plays National Grid (LSE: NG) and Centrica (LSE: CNA), in previous periods of severe market volatility, would have chugged higher in lockstep as investors piled into ‘defensive’ stocks.

The indispensable role of electricity nowadays has traditionally given suppliers the type of earnings visibility that most other firms can only dream of, a particularly important quality for investors seeking ports in an intensifying storm.

But the goalposts are increasingly changing in this industry, a scenario that has seen a growing divergence between National Grid and Centrica’s share price movements. While the former has chalked up a 1% gain since the turn of January (defying a 10% decline in the wider FTSE 100), Centrica has seen its share value erode 14%.

Supplier on the slide

This comes as little surprise given the waves of bearish news striking the British Gas operator. Scottish Power, E.On and SSE have all cut their gas prices by more than 5% in recent weeks, and Npower got in on the act on Monday by promising to slashing its standard gas tariff by 5.4%.

This raises the heat on Centrica to implement more revenue-sapping price reductions of its own. An increasingly cut-throat environment — fuelled in no small part by the rise of the independent supplier — has been relentlessly chipping away at the British Gas customer base for years now and account numbers are expected to have slipped again in the last quarter.

Centrica also faces the implications of a tanking oil price at its Centrica Energy upstream division. Brent values have marched back towards the multi-year troughs of $27.67 per barrel struck in January thanks to renewed concerns over a growing supply imbalance.

A defensive dynamo

Conversely, National Grid’s vertically-integrated model means that it doesn’t face the same crippling competitive pressures casting a pall over Centrica’s earnings outlook. And while the ‘Big Six’ suppliers also face the possibility of profit caps from Ofgem, the hand of the regulator is actually helping National Grid as RIIO price limits the amount of capital seepage at the business.

The picture isn’t all rosy over at National Grid as the costs of maintaining its network on both sides of the Atlantic are colossal. But the huge investment the firm is making to improve its asset base should continue to keep earnings rising well into the future, in my opinion.

So which would I buy?

Not surprisingly I believe National Grid is the superior power play for defensively-minded investors. Firstly, expected earnings bounces of 4% and 1% in the years to March 2016 and 2017, respectively, leave the business dealing on excellent P/E ratings of 14.9 times and 14.7 times.

And dividend investors should be attracted by projected payouts of 43.7p per share for this year and 44.7p for 2017. These figures yield 4.8% and 5%, respectively.

In stark comparison, Centrica is expected to follow a projected 8% earnings decline for 2015 with a marginal drop in the current period, leaving the business on a prospective P/E rating of 12 times. While this figure is undoubtedly decent on paper, I don’t believe it’s low enough to fairly reflect the company’s high-risk profile.

The City expects Centrica to build dividends again from this year following a second successive dividend cut in 2015 — a forecast payment of 12.4p for this year yields a brilliant 5.9%. But I can’t see this scenario materialising as earnings drag and debt levels climb.

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Royston Wild has no position in any shares mentioned. The Motley Fool UK has recommended Centrica. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.