Basically the new Corsair RM series modular power supplies replaced the TX series. It’s like an upgraded version of the TX lineup. The RM series features 80 Plus Gold certification, just like the HX series. But RM series comes with more wattage options and cheaper price tag compared to the HX and AX series.
Despite having similar features, the Corsair RM and HX are not made by the same manufacturer and they are not made with the same components. If the RM series comes with the cheaper price tag, this indicates that manufacturing cost is most probably cheaper as well than the HX series, and this might be due to the fact that the components used to manufacture the RM series are not the same with the HX and AX series.
Of course, there are other differences and some features that the RM series does and doesn’t have. For example; among the RM, HX and AX series only the HX series is not the fully modular PSU. Both RM and AX are full modular. I think the cables used are also not the same.
Meanwhile, the Corsair AX series remains as the top of the line modular power supply. It’s 80 PLUS Platinum certified and has features that both the RM and HX series doesn’t have. Not to mention, the AX series are built for high to extreme performance and are designed to handle extreme situations.
If we were to rank these three modular PSUs, the Corsair AX will be on top, followed by the HX series and then the RM series. The RM series are geared towards budget enthusiasts and system builders who are looking for a cheaper alternative than the HX series. So if you don’t overclock or if you do mild OC only, and you don’t have lots of power-hungry components installed in your system, the RM series would be enough for you. Meanwhile the HX and AX series are geared towards mainstream and high end users who really push their system, or have lots of components installed. Compared to a generic power supplies, the RM still series is still a better option IMHO. Below is a table comparing their different manufacturer’s suggested retail prices.