We generally do not recommend using these adapters. Please read the articles below for additional detail.
If you want to geek out on why junky serial to USB adapters are a terrible idea US Converts has a great article on the topic:
If you need them - you absolutely need to buy them from these guys. Here's the product to purchase:
Please note: we do not support these adapters when using the Cloud Retailer POS Software. In most cases, the billable time spent needed to make these adapters work exceeds the cost of buying a new receipt printer or similar piece of hardware.