Dozens of investment firms will return more than $125 million to their clients after revealing to U.S. regulators that they peddled higher-fee mutual funds when lower-priced options were available.

Units of Wells Fargo & Co., Royal Bank of Canada and Raymond James Financial Inc. were among 79 investment advisers that didn’t adequately inform customers they would be pushed into funds with higher fees, the Securities and Exchange Commission said in a March 11 statement. The firms avoided fines because they self-reported the alleged wrongdoing to the agency.

The SEC settlements involved so-called 12b-1 fees, controversial charges that mutual-fund companies...