If you’ve worked for a big corporation, you’ve probably looked on with a mix of amusement and disgust as the bosses chased one fad after another.

One day they’re chasing “synergies” by rolling out products that have little to do with the main business.

Then they reverse course to get back to their “core competencies” — whatever made them successful in the first place.

Often, the folly of flip-flopping is obvious to the younger, hipper employees who understand the changing marketplace better than the older folks in charge.

So a lot of employees at American Express and Citigroup must be shaking their heads these days.

A few years ago, both companies bought into the fad of the day — the idea of the one-stop financial supermarket. Now they’re changing course.

American Express announced Tuesday that it would spin off its financial-advice business to focus on its core competency, credit cards. A day earlier, Citigroup said it would sell its insurance and annuity business to MetLife.

Citigroup was formed by the late-’90s merger of Travelers Group, an insurance and brokerage company, with Citicorp, which specialized in banking and credit-card products.

This and similar moves at other companies were designed to offer customers one-stop shopping for financial services. Customers, it was thought, would get mortgages and insurance from the same company that held their brokerage accounts.

Not everyone thought that would happen. At least one commentator asked, “Is this something ordinary consumers really yearn for — or need?”

That was me, in an April 1998 column. My point back then was that consumers ought to shop around for various financial services, and that doing so would only get easier with the Internet.

It has.

There’s just no reason to get a mortgage, life insurance and credit cards from the same company that provides your mutual funds. You should look for the best deal with each.

What I did not foresee were the scandals that would hit the insurance, mutual fund and brokerage industries in the new century.

At the heart of all those was conflict of interest. Customers who sought investment advice from their financial supermarkets, for example, were too often steered to the company’s in-house mutual funds, even if competitors’ funds would have suited them better.

Citigroup was among a number of Wall Street firms to pay big fines in the conflict-of-interest scandal involving analysts’ stock recommendations. American Express paid a fine for not giving big mutual fund investors discounts they were due.

Consumers have — quite understandably and correctly — become more skeptical and alert to conflicts of interest.

At the same time, they’ve become more tech-savvy, using the Internet to shop for financial services and other products nationwide. Consumers today know there’s no need to favor a neighborhood bank when shopping for a mortgage or certificate of deposit — not if a provider from across town, or across the country, offers a better rate.

Back in the ’90s, the financial-supermarket advocates thought customers would like the convenience of seeing all their financial affairs reported on a single monthly statement. But that wasn’t much of a draw, since you can view all your accounts at once — no matter how many providers you use — with an Internet-connected program such as Quicken.

In fact, some brokerages and fund companies offer services that track the customer’s accounts with other providers. Go to one Web site to see all your holdings at Bank A, Fund Company B and Brokerage C.

Of course, the idea of the financial supermarket is far from dead: It’s hard to kill a fad when billions of dollars have been spent on it.

Happily, though, many ordinary folk have proven they know better than the big boys who run these conglomerates. The financial supermarket was, and is, a lousy idea.