The key consideration is to figure out what is the maximum voltage and maximum current you need for your applications. Typically there is no need to pick a model that has higher rating than your maximum voltage and current, except in the case of high power application, where we recommend you to go up one notch in current rating, e.g., if your application requires maximum of 30V and 15A, the model HY3020E should be sufficient; on the other hand, if your application requires output of 28V and 20A, it might be a good idea to get the model HY3030E instead. Other things to consider include the type of displays (LCD or LED), single or multiple outputs, etc. The current industry trend is to move away from LCD displays to LED displays, as bright LED displays are now widely available at comparable cost. Color LED displays are also available from Mastech with models like 3005F-3 and 3003F-3. If you do a lot of circuit design and testing, triple output DC power supplies are a plus as they provide two variable outputs plus a third output at 5V fixed; the two variable outputs can be operated at independent, series or parallel mode, providing a very wide range of voltage and current.