The ETL marking process involves many of the same tests that UL, CSA or CE would require.
The ETL mark was created in 1896 when Thomas Edison founded Electrical Testing Labs (ETL) The ETL mark process involves many of the same tests that UL, CSA or CE would involve and is accredited by many of the same regulatory bodies, so it is accepted broadly throughout North America and other parts of the world.
By having the ETL mark on your product, you are indicating that it has gone through the applicable testing associated with national standards, and the product was complaint. The ETL mark is given extra legitimacy by being a NRTL (Nationally Recognized Testing Laboratory). An NRTL is an independent laboratory recognized by OSHA as being able to test products to specific product safety standards.