Corsair has been in the business of providing PC power supplies since 2006, starting with the "HX Series".

The letters don't really mean anything, so it can be really confusing which Corsair PSU is better than another. 

To further complicate things, a number of the series names get "recycled". Often, with improvements. For example, the HX started as a semi-modular 80 PLUS Standard PSU. It's evolved into an 80 PLUS Bronze, then Silver, then Gold, and then eventually became a fully modular 80 PLUS Platinum PSU.

AX has evolved as well. Once an 80 PLUS Gold, fully modular PSU, it evolved to a Platinum and now an 80 PLUS Titanium power supply.

Some series don't evolve much. RMx, for example, changed platforms, but the performance remained the same.

I put this list together. The PSUs below are ranked from "high end" to "low end".

I'm starting with the PSUs currently in the market:

AX1600i: Titanium efficiency, fully modular, FDB fan with Zero RPM fan mode. All Japanese caps. Rated at 50°C. All analog ICs replaced with MCUs (fully digital). PSU has monitoring capability via LINK or iCUE. Has a very unique bridgeless totem-pole front end with GaN transistors. Complete AX1600i specficiations
HXi: Platinum efficiency, fully modular, FDB fan with Zero RPM fan mode, analog PSU, but with monitoring. All Japanese caps. Rated at 50°C. Note the "old school" livery. HXi is the oldest PSU in the Corsair line up. Why mess with perfection? Complete HXi series specifications
HX: Platinum efficiency, fully modular, FDB fan with Zero RPM fan mode, analog PSU w/o monitoring, but a switch to choose between single and multiple +12V rail. All Japanese caps. Rated at 50°C. Complete HX Platinum series specifications
RMi: Gold efficiency, fully modular, FDB fan with Zero RPM fan mode, analog PSU, but with monitoring. All Japanese caps. Rated at 50°C. Complete RMi series specifications
TX-M: Gold efficiency, semi-modular, rifle bearing fan w/o Zero RPM fan mode. All Japanese caps. Rated at 50°C. Complete TX-M Gold series specifications
RMx (new): Often called "RMx 2021". Gold efficiency, fully modular, MagLev bearing fan with Zero RPM fan mode. Supports new Modern Standby Mode and meets new 2% efficiency requirement of 70%. All Japanese caps. Rated at 50°C.
RM (new): Often called "RM 2021". Gold efficiency, fully modular, Rifle bearing fan with Zero RPM fan mode. Supports new Modern Standby Mode and meets new 2% efficiency requirement of 70%. No promise of Japanese caps. Lower hold up time than RMx. Rated at 50°C.
RM (new) in White: Often called "RM 2021". Same as above, but with white paint and cables.
CX-F RGB: Based off Vengeance Silver (below). Added RGB lighting reduces efficiency to Bronze. Fully modular, rifle bearing fan. Supports push button RGB, ARGB and iCUE. Japanese primary capacitor. Rated at 40°C.
CX-F is also available in a white housing with white sleeved and flat cables.
CX: Bronze efficiency, non-modular, rifle bearing fan. Only Japanese bulk cap. Rated at 40°C. Unlike the semi-modular version, CX-M, this one has a resonant LLC platform. Complete CX (2017) series specifications CX & CX-M "cheat sheet" (comparison of different generations)
CX-M: Bronze efficiency, semi-modular, rifle bearing fan. This, the CV, and the VS series are the only Corsair PSUs that aren't resonant LLC and have a double forward front end. That said, CX-M at least has MOSFET SR, DC to DC for the +3.3V and +5V, where VSand CV450 and CV550 do not. Only Japanese bulk cap. Rated at 40°C. Complete CX-M (2015) series specifications CX & CX-M "cheat sheet" (comparison of different generations)
CV650:  New.  Bronze efficiency, double forward with DC to DC for the +3.3V and +5V. Complete CV series specifications
CV450 & CV550: Simply nothing more than VS (see next bullet), but with Bronze efficiency. Sleeve bearing fan, no Jap caps, double forward, group regulated 12V and 5V. Complete CV series specifications
VS: Regular 80 PLUS efficiency. Non-modular. Sleeve bearing fan. No Japanese caps. Rated at 30°C. Double forward and no DC to DC (group regulated 12V and 5V, mag amp 3.3V). #50W units meet ErP 2013 efficiency requirements. #00W PSUs do not and are only sold in regions other than the EU. Complete VS (2018) series specifications

SFX PSUs:

Corsair SFX PUSs are true SFX form factor and not the "unofficial" SFX-L form factor.  They also come with very short cables because they're made for ITX builds.

SF Platinum:  80 PLUS Platinum, fully modular, rifle bearing fan. Complete SF Platinum series specifications
SF Gold:  80 PLUS Gold, fully modular, rifle bearing fan. Complete SF Gold series specifications

Older versions of the series names currently in production (the series has been updated, but they use the same name):

AXi: Used to be a full line of Platinum digital power supplies with DBB fans. Complete AXi (old version) series specifications
AX: Titanium efficiency, fully modular, FDB fan with Zero RPM fan mode, analog PSU w/o monitoring. All Japanese caps. Rated at 50°C. These PSUs use a LLC resonant front end and DC to DC for the +3.3V and +5V rails. Complete AX Titanium series specifications
AX: Used to be Platinum efficiency with DBB fan. Complete AX Platinum series specifications
AX: Used to be Gold efficiency with DBB fan. The original Gold AX was Corsair's first fully modular Gold PSU.
HX: Used to be Gold efficiency and semi-modular. DBB fan. Complete HX Gold series specifications
HX: Used to be Silver efficiency and semi-modular. DBB fan.
HX: Corsair's original PSU series. Originally 80 PLUS (standard) efficiency. DBB fan.
RMx: Often called "RMx 2018". Gold efficiency, fully modular, rifle bearing fan with Zero RPM fan mode. All Japanese caps. Rated at 50°C. From here on down, all of the PSUs are analog without any kind of monitoring or control via Corsair Link or iCUE. The current RM1000x uses the old generation platform as the new platform maxes out at 850W. Complete RMx (2018) series specifications
RMx was also available in a white housing with white sleeved and flat cables. Complete white RMx series specifications
TX: A totally overbuilt for a Bronze PSU with DBB fan. The 650W was built by Seasonic, the 750W and 850W were built by CWT.
TX850: The highest wattage of the early, non-modular TX PSUs. Made by CWT and is 80 PLUS Silver.
TXV2: Second generation non-modular TX, now 80 PLUS Bronze efficiency, based off the Seasonic S12II platform.
TX-M Bronze: First version of a semi-modular TX-M. 80 PLUS Bronze efficiency. These were made by CWT.
RM: Often called "RM 2019". Gold efficiency, fully modular, rifle bearing fan with Zero RPM fan mode. Supports new Modern Standby Mode and meets new 2% efficiency requirement of 70%. No promise of Japanese caps. Rated at 50°C. Complete RM (2018) series specifications
RM: Often called "RM 2013". Prior to the most recent RM and before the RMx and RMi, It only had a Japanese bulk cap and was only rated at 40°C. It did have an I2C connector that reported +12V rail load and fan speed to Corsair LINK. This was also the first Corsair PSU to use an MCU to incorporate a Zero RPM fan mode.  Prior to this, an analog controller was used in both the AX Gold and second generation GS that was problematic due to using only temperature to determine if the fan should spin or not. It should be stated that there was a thermal issue with the early Chicony made 750W and 850W units that caused the PSU to shut down even when temperatures were below 40°C when the PSU was mounted in the chassis with the fan down. This was due to a thermistor placement on the PCB. The heat would "rise" into the thermistor and the PSU would OTP. This was remedied in PSUs built after 41st week of 2013. Complete RM (2013) series specifications
Vengeance: Silver efficiency, semi-modular, rifle bearing fan. Has a switch to choose between single and multiple +12V rails. All Japanese caps. Rated at 40°C . Complete Vengeance Silver series specifications
Vengeance Bronze: 80 PLUS Bronze efficiency. Came in fixed cable and semi-modular versions. Double forward topology. Is literally the same platform as CX-M. Rifle bearing fan w/o Zero RPM fan mode. All Japanese caps. Rated at 40°C. Replaced by Vengeance Silver.
Previous generation CX: These 80 PLUS Bronze PSUs were double forward, based off of CWT's DSAIII platform (except 750W, which was PUQ-B based), but did have DC to DC for the +3.3V and +5V. Rated at only 30°C and has a sleeve bearing fan. Three year warranty.
CX with no 80 PLUS: Based of of DSAII. Double forward, group regulated, rated at 30°C and sleeve bearing fan. Three year warranty. There was actually two "versions" (the newer called "V2") but I do not know the difference because they're both based off of the DSAII. The older one did only have a two year warranty.
Original CX-M: Essentially modular versions of the original CX Bronze units. So, double forward with DC to DC for +3.3V and +5V.
Original VS Series: These were 230V Only PSUs (would only work with 180V to 240V mains). Sleeve bearing fan and a .3mm thick steel housing (context: PSU housings are typically .5mm thick). Sleeve bearing fan. 3 year warranty.

Completely discontinued series (not made any more and series names not reused):

CS-M: Resonant LLC. Gold efficiency, semi-modular, rifle bearing fan w/o Zero RPM fan mode. Only Japanese bulk cap. Rated at 40°C. Replaced by TX-M Gold.
GS: Double forward. Has an R- G- B- fan that could be changed with a push button on the housing.  The first was just 80 PLUS efficienct.
GS: Double forward. Has an R- G- B- fan that could be changed with a push button on the housing. The second generation was 80 PLUS Bronze.
GS 2013 Edition: Double forward. Has an R- G- B- fan that could be changed with a push button on the housing. This generation is also 80 PLUS Bronze and had a crude, analog version of a zero RPM fan mode.
VX: Double forward. Was cheaper than HX, but still built like a tank and too expensive, so it didn't last long in the market. The 450W was a Seasonic S12II platform while the 550W was CWT's PSH platform.