Introduction

I usually avoid reviewing products that are not available on the market, but this rule is for EOL products and not those that haven't been released yet, this is why I'm making an exception for the CSX 850M-G SFX OEM PSU, which will soon be available under more well-known branding. This model is at the end of the development phase, a good opportunity for me to show you the near-future of high-capacity SFX PSUs with PCIe 5.0 connectors. Despite compact dimensions, SFX PSUs get stronger and more refined by the day, but this also affects performance and noise output, so there is a Wattage line that shouldn't be crossed; else, both factors will suffer.

CWT's upcoming CSX (M) line will consist of four members with 650 - 1000 W capacities, all featuring 12+4 pin PCIe connectors, supporting forthcoming GPU generations. Investing in a PCIe 5.0 compatible PSU will become essential, given the new 16 pin connector, along with changes it brings, renders the majority of existing PSUs incompatible with next-gen GPUs from NVIDIA and AMD. It is uncertain whether upcoming GPUs will be partially compatible with the non-ATX 3.0 ready PSUs or their power needs will require 12+4 pin connectors and ATX 3.0 (which includes PCIe 5.0) compatibility. Another thing you shouldn't confuse is PCIe 5.0 and ATX 3.0 compatibility. A PCIe 5.0 ready PSU is not automatically ATX 3.0 ready, but the other way around is correct. An ATX 3.0-ready PSU is also PCIe 5.0 compatible.

Specifications

Photos

There is no power switch, which is a con in my book.


The power specifications label is at the bottom, covering most real estate.


The modular board has eight sockets.


The exterior design is plain because this PSU is an OEM design. Brands will likely customise the case.


Here are more photos of the PSU from various angles.

Cables and Connectors

Plenty of cables and connectors are provided, but you cannot have all of them connected simultaneously. Most included cables are short, since the PSU is designed for small chassis.


This is the PCIe 5.0 cable/connector that makes the PSU stand out from the crowd, providing compatibility with upcoming GPUs.


The lack of 4-pin Molex connectors looks strange. But brands can modify cable configurations, including 4-pin Molex, most likely.


The unit's AC power cord.

Component Analysis

Before reading this page, we strongly suggest looking at this article, which will help you better understand the insides of a PSU.



This is a new platform by CWT, with the code name CSX. The primary heatsink is large enough; on the secondary side, there are no proper heatsinks, so the PCB doesn't look overpopulated. The design is up to date, and the components that CWT use are of decent quality. You can ask for better caps on the secondary side to replace those ChengX ones if your budget allows it. The problem is that it is tough to find good caps at fair prices during this period because of the vast stock shortages.


The transient filter is complete.


There is an MOV for protection against power surges. An NTC thermistor handles inrush currents. It is supported by a bypass relay.


The two bridge rectifier can handle up to 50 A!


The APFC converter uses a single, powerful Infineon FET and a strong boost diode. Lastly, the bulk cap is Rubycon, and is of high quality.


CWT installed a FET to isolate the APFC converter once the PSU is in standby mode, to reduce vampire power.


The primary switching FETs are installed into a half-bridge topology. The choke shown in the second photo is the resonant tank.


The resonant controller is a Champion CU6901VAC, which supports kick (burst) mode operation, for high efficiency even at very light loads.


The board holding the +12 V FETs is installed next to the main transformer for minimized energy losses.


I don't have a problem with Elite caps. On the contrary, I am not fond of the ChengX ones. This is an OEM platform, though, and the client brands can ask for any changes in parts, especially in filtering caps, which can notably affect production cost.


The DC-DC converters live on a daughter board.


The standby PWM controller is an On-Bright OB2365T.


The supervisor controller is a Weltrend WT7502R.


A substantial number of polymer caps are installed on the modular board, suppressing ripple on all rails.


Soldering quality is not the best I have seen by CWT, but this is not an MP (Mass Production) product.


The cooling fan is by Hong Hua and uses a fluid dynamic bearing. The fan size is ideal for an SFX unit.

Test Setup