Corsair RM850e ATX 3.1 (2025) PSU Review

1. Introduction2. Bundle & Cabling3. External4. Internal5. Testing Methodology and Results6. Closing Thoughts7. View All Pages

Following on from our recent review of the Corsair RM1000e, today we take a look at the 850 watt version in the new range – the RM850e. This is another fully modular power supply with native 12v-2×6 connectors to power the latest graphics cards. These are not the Corsair flagship models so they come with a more limited 7 year warranty.

There are three power supplies in this new range, a 750w, 850w and 1000w unit. The 1000W supply scored well in our testing and you missed that review then head over HERE.

UK prices from Corsair directly indicate that only £10 price difference exists between the 750 watt and 850 watt models, while the 1000W model is £35 more expensive. As we previously mentioned, all models have a 7 year warranty in place which falls some way from the leading 12 years on some of the platinum models we have reviewed lately. This is one of the tradeoffs when you move down a companies product stack but for most people it will be fine.

Key Features:

• Fully Modular PSU: Reliable and efficient low-noise power supply with fully modular cabling, so you only have to connect the cables your system build needs.
• Cybenetics Gold-Certified: Steady power output at up to 90% efficiency, ensuring lower power consumption and cooler temperatures.
• Native 12V-2×6 Connector: Power the latest high-end graphics cards out of the box – no adapter needed.
• Intel® ATX 3.1 Certified: Compliant with the ATX 3.1 power standard, supporting PCIe 5.1 platform withstands 2x transient power excursions from the GPU.
• Embossed Cables with Low-Profile Combs: Sleek, ultra-flexible embossed cables look great and make and connecting the RMe a breeze, even in tight spaces.
• Keeps Quiet: A 120mm rifle bearing fan with a specially calculated fan curve keeps fan noise down, even when operating at full load.
• 105°C-Rated Capacitors: Delivers steady, reliable power and dependable electrical performance.
• Modern Standby Compatible: Extremely fast wake-from-sleep times and better low-load efficiency.
• Zero RPM Fan Mode: For near-silent operation at lower loads.
• The Right Fit: Compact 140mm-long casing ensures an easy fit in modern enthusiast PC cases.
• Resonant LLC Topology with DC-to-DC Conversion: Provides clean, consistent power and ensures better energy-efficiency across a wide range of loads.
• Seven-Year Warranty: Your guarantee of reliable operation for peace of mind through multiple builds.

Corsair box artwork is always very distinctive – and they stay true to their history of yellow coloured panels across all sides. On the front of the box we have two Cybenetics logos for Gold efficiency and A power ratings. Good to see Corsair dropping focus on the older 80 Plus ratings.

Rear of the box highlights some key selling points, such as support for the latest graphics cards, the efficiency and fully modular cabling. Some graphs at the bottom highlight power efficiency and fan noise levels.

Accessories in the box include a regional specific power cable, some cable ties, literature and mounting screws. The packaging is pretty good and the box should protect the PSU during shipping well.

We like these new Corsair cables – they call them embossed. I would call them individually sleeved. They look great and this 850W unit has plenty of cables to suit a variety of system builds targeting this power demand.

These new supplies are fairly compact in size, measuring 160x150x86 mm. The quality of the paint is good and the styling is neutral in colour with all the logos and badges in silver/white on the sides of the chassis.

The grille at the top of the unit is heavily stylised with a Y logo shape to allow for airflow. As I mentioned in the last video its not the best possible venting for airflow in my opinion but it didn't seem to greatly impact the 1000W unit when we tested it.

The modular bay is split into a traditional Corsair way across two vertical rows, separated into panels.

The power side is home to the power connector and power switch and the vented panel which aids with airflow from the unit inside.

This unit is able to deliver 70.8A across the primary single +12V rail. Both +3.3V and +5V minor rails can deliver 20A.

Corsair are using a Hong Hua 120mm fan model number HA1225H12SF-Z. This is a rifle bearing fan rated 12V 0.58A. You can buy these fans online for around £10. As I mentioned in the last review these fans are not as high grade as the Fluid Dynamic bearing models that Hong Hua make, featured in more expensive units.  There are certain trade offs when you move down a product stack a little.

As with the 1000W unit we reviewed a while ago, the OEM for these units is HEC. This is a half bridge topology on the primary side with an LLC resonant converter. The secondary side uses a synchronous rectification system for the +12V rail which powers a pair of VRMS to create the minor rails.

The PCB inside is quite small and densely populated with several large heatsinks to aid with cooling – this makes sense with vertical PCB boards mounted to the main one. One of the boards is home to the DC-DC converter to generate the minor rails.

Soldering quality is high throughout and the main PCB exhibits great attention to detail in this regard. I was a little disappointed to see a Taiwanese TEAPO primary capacitor used in this unit, rated 400V 470uF (down from 680uF in the RM1000e). I had some bad experiences with TEAPO caps many years ago, so I am hoping they are better in 2025. On a plus point, this primary cap is rated 105c, not 85c.

This unit ships with OCP, OVP, SCP, OPP and OTP protections.

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 Watt DC load. We run at 35c in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

We test in a single +12V configuration.

DC Output Load Regulation
Combined DC Load	+3.3V		+5V		+12V		+5VSB		-12V
	A	V	A	V	A	V	A	V	A	V
85W	0.95	3.33	0.92	4.99	6.00	12.04	0.50	5.01	0.20	-12.00
170W	1.70	3.33	1.67	4.98	12.35	12.04	1.00	5.01	0.20	-12.00
425W	3.00	3.33	3.05	4.98	32.20	12.03	1.50	5.01	0.30	-12.00
640W	4.05	3.29	4.05	4.98	49.00	12.01	2.00	5.01	0.30	-12.00
850W	5.00	3.28	5.23	4.98	65.52	12.00	2.50	5.00	0.50	-12.01

Load regulation is really good on all the rails but we noticed some dips on the +3.3V rail.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing	+3.3V		+5V		+12V		-12V		+5VSB
	A	V	A	V	A	V	A	V	A	V
760W	1.0	3.33	1.0	5.00	60.0	12.00	0.2	-12.01	0.50	5.01
165W	15.0	3.26	18.0	4.96	2.0	12.02	0.2	-12.00	0.50	5.00

The power supply coped fairly well, but there is some noticeable droop on the +3.3V rail which could be improved

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum.

ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output	Ripple (mV p-p)
+3.3V	50
+5V	50
+12V1	120
+12V2	120
-12V	120
+5VSB	50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load	+3.3V	+5V	+12V	5VSB
100W	5	7	11	15
225W	6	9	16	18
450W	11	12	21	21
675W	14	14	27	24
850W	16	15	36	29

Noise suppression is strong across all the rails. Specifically on the minor rails.

Efficiency (%) 240V
100W	89.3
225W	91.4
450W	93.2
675W	92.1
850W	91.4

The efficiency results are really good, peaking at around 93% between 45-55% load, and dropping to around 91.5% at full load. An impressive set of results.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the power supply we have taken it into our acoustics room environment and have set our Digital Sound Level Noise Decibel Meter Style 2 one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide

10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refrigerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
100W	<28
225W	<28
450W	31.3
675W	34.2
850W	39.1

The fan remains inactive at lower power demands with some action appearing once the power demand exceeds 300 watts. PSU noise rises and becomes audible around 650 watts load. At full load the fan is clearly working quite hard to help maintain temperatures and stability.

Temperature (c)
	Intake	Exhaust
100W	37	40
225W	38	42
450W	40	44
675W	45	53
850W	46	58

Temperatures inside the chassis remain relatively cool even at higher load levels. The fan at higher demands really helps ensure the temperatures never become a problem at the cost of noise emissions.

The Corsair RM850e is a decent performer in our tests over the last week, although I was slightly more impressed with the RM1000e I reviewed a short while ago. I also think that with the £10 price reduction Corsair have applied to the RM1000e (to around £150) that it provides a little more potential future proofing if you decided to upgrade down the line to a more powerful graphics card and processor.

I mentioned in my last video that the RM1000e would be a good partner for the new RTX50 series of cards and the RM850e is no different – you would just need to ensure you don't decide to partner it up with a new RTX5090 as we found in our launch review that this card can demand close to 600 watts of power (READ HERE). Combine this with a power hungry processor and you would be asking for problems. In the real world the RM850e would be better suited to the upcoming 5070ti.

Our review of the new Nvidia RTX5080 is live very soon as we publish this review and in theory it will demand in and around 350-400 watts so the RM850e should work fine. You just need to weigh in the demands of whatever processor you may be using as well.

This unit coped well with our cross load test and load regulation was pretty good across the rails – with just a dip visible on the +3.3V rail. Nothing that would cause any issues, just worth mentioning. Also we feel the +12 rail could deliver slightly better noise suppression at the higher end of the power demand graph, but again this is well within industry rated parameters so we are splitting hairs.

The MSRP for the RM850w is £124.99 (HERE) in the United Kingdom (other prices are listed on the first page of this review if you are outside the UK). Personally I would rather spend the extra £25 and get the RM1000w which is on offer for £152 (HERE).

Pros:

• Great load regulation.
• Rifle bearing fan is relatively quiet for most of the load demand.
• Soldering quality is high.
• efficiency is good.
• cable quality is great.
• fully modular.

Cons:

• Fluid dynamic bearing fan option would be nice.
• Taiwanese Teapo primary cap.
• 7 year warranty could be a little better.

Kitguru says: The RM850e power supply will make a good partner for a new 5070 ti or 5070 graphics card. It is built to high standards at a fairly reasonable price point in the UK at around £125. 

Become a Patron!