UL has nothing to do with reliability or size or function. It's point is to prevent fire and electrocution.

Keith Cress
kcress - http://www.flaminsystems.com

UL is one of several recognized third party type certification authorities.
UL, CSA are the ones most recognized in North America, there are a few others.
UL drafts safety standards, and operates testing laboratories where manufacturers pay to have their devices tested to meet the standards.
https://www.ul.com/
https://www.csagroup.org/

The CE mark is a very different kind of thing

Quote (https://asq.org/quality-resources/ce-marking)

The presence of CE marking further indicates that appropriate technical documentation supporting the use of the mark is available and can be provided by the manufacturer, importer, or person responsible for placing the product on the EU market upon request.
CE marking does not provide any specific information to the consumer. It is not a quality assurance declaration, it does not show evidence of third-party testing, and it should not be confused with any independent certification mark of the type issued by international or European notified test bodies.

Generically, UL is what we call an "NRTL", for Nationally Recognized Testing Lab, of which they and CSA are the most well known. Here is a list of accepted NRTLs maintained by the US Dept. of Labor, OSHA office.
https://www.osha.gov/nationally-recognized-testing...

The requirement for NRTL listing is also codified on a state-by-state basis, with the majority of US states requiring some form of NRTL listing for electrical equipment (if such a listing exists), using that OSHA list as a reference. In addition, many NEC articles require specific devices to be "listed" for acceptance, or otherwise requiring significant and onerous testing / acceptance processes if not. So in effect, trying to provide unlisted equipment to the US results in difficulty for installers to get approval when seeking permits or being inspected. In addition, many insurance companies here will have a requirement for all electrical equipment to be listed by an NRTL, otherwise they can deny payout for a loss associated with them.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

In some cases UL and non-UL listed items might come off the exact same assembly line. In other cases the products may be quite different. Utilities buy a variety of non-UL listed equipment.