Suggestions for USB-serial conversion

[Controls_Engineer79]

Hey there guys, i don't know if this question has been raised previously and is just buried in the mass of postings this forum recives but heres my question:

As you know most (if not all) new computers and laptops now come without a RS-232 serial port, but most PLCs still have not updated to having USB ports (with the exception of some new omron models) the question i have is this, do any of you have any suggestions as to what brand of USB-serial converter i should buy?

I used to work as a inside technical support and application engineer for Omron in Toronto, and that was a common issue that people would contact me for, that their store-baught USB converts could not connect to the plcs. Now i know that Omron markets their own USB converter thats designed to work with all omron brand products, but as far as i know allen bradley has not done the same.

So does anyone out there have a list of USB converters that you know work for Allen bradley series plcs and HMIs - and siemens plcs and HMIs???? or maybe a list of USB-serial converters to avoide because they dont work?

Its always been my understanding that the problem with these converters is that theres no standardized comm protical, different manufactures use different comm proticals, this creates a "hit or miss" result when buying these things.