Janet Yellen is discovering that when it comes to providing monetary stimulus, the Federal Reserve is damned by emerging markets when it does and damned when it doesn't.

Sixteen months after she used a Tokyo gathering of global policy makers to defend her institution against criticism it was purchasing too many assets, Fed Chair Yellen attends this week's Group of 20 meeting in Sydney being lobbied to pay greater attention to foreign fallout as the U.S. slows its bond-buying.

What's not changed is her response: A well-managed U.S. economy benefits the world and other central banks have tools to support their own economies. That's disappointing counterparts such as India's Raghuram Rajan and Gill Marcus of South Africa, who criticized the lack of a synchronized global monetary policy as developing-nation currencies suffer their worst start to a year since 2010.