NZXT is a company that has come from fairly humble origins, starting things off back in 2004 with just a couple of PC cases. They have come a long way since then, slowly by surely expanding their ever-growing product portfolio. Nowadays, NZXT is one of the most prominent PC case, cooling, and power supply manufacturers, with a very strong global market presence.

We have reviewed several NZXT products in the past, yet very few of their PSUs ever found their way into our labs – in fact it's been nearly a decade since our last NZXT PSU review. That counter resets today, as we are taking a look at NZXT’s latest upper-class PSU design, the C-series C650.

Among NZXT's PSU lineup, the C-series is very much the manufacturer's bread and butter for PSUs, with C-series PSUs making up the vast majority of its product lineup. At a high level, the C-series is designed for advanced PC users and enthusiasts alike, and with the rest of NZXT's lineup only going higher still, it's clear that the company is taking aim at a specific niche of the PSU market rather than going after a broad swath of the PSU market. Along these same lines, NZXT has also dialed in to the middle of the market in terms of capacity; with three C-series models ranging from 650 Watts to 850 Watts, the PSUs fall into a typical range for today's high-end single CPU/single GPU systems.

As for our review, today we'll be taking a look at the least powerful unit of the series the 650 Watt C650.

We received the NZXT C650 PSU in a relatively simple cardboard box. The artwork on the box is simplistic, yet appealing, with just a beautifully taken picture of the unit decorating the front side of the box. Its thick cardboard walls and internal foam padding provide adequate shipping protection.

NZXT stuck to the basics when it comes to the C650, supplying only four mounting screws, some modular cables, and an AC power cable alongside the PSU. The modular cables do however come inside a simple purple bag, so they can be contained. Otherwise there are no cable straps, cable ties, or other accessories of any kind.

The NZXT C650 PSU is a fully modular design, meaning that no cables are hardwired to the chassis. All of the cables are made of all black wires and black connectors. The SATA and Molex cables are “flat” type cables, with exposed wires that are attached to each other, while the PCI Express, CPU, and 24-pin ATX cables have nylon sleeving covering the wires.

External Appearance

NZXT designed the C650 to be aesthetically subtle and functional. The chassis is entirely black, with the company logo and product name printed with dark reflective fonts on its two sides. A black sticker with the unit’s electrical certifications and specifications can be found on the top side of the chassis. Other aesthetic improvements are limited to simple chassis upgrades, such as rounded edges and an integrated fan finger guard. Although the PSU is 150 mm deep – a little longer than what the ATX standard dictates (140 mm) – it is compatible with the vast majority of ATX-compliant cases available. Only very few proprietary case designs may cause compatibility problems.

At the rear side of the PSU, we can see the typical AC cable receptacle and on/off switch, as well as a toggle switch that controls the cooling fan mode. The C650 has two cooling modes – the basic mode, where the fan spins constantly and its speed is thermally controlled, and the hybrid mode, where the fan can stop spinning entirely when the load is low enough that active cooling isn't necessary. Some users are uncomfortable with zero active cooling or rely on the PSU’s airflow for other reasons, therefore the option to disable the hybrid mode was a good idea.

Modular connectors cover most of the PSU’s front surface. A basic legend is directly printed onto the chassis, along with a warning not to use cables from other manufacturers. The connectors are keyed, ensuring that it is not possible to insert the wrong cable into the wrong receptacle. 

Internal Design

The NZXT C650 relies on a 120 mm fan for its cooling needs, which is the largest fan that could fit inside its chassis. It employs a simple black 120 mm fan that is made by Hong Hua, a known but not very popular manufacturer. In fact, these fans aren't even used by very many OEMs, instantly hinting at the OEM behind the creation of the C650. The HA1225H12F-Z has a fluid dynamic bearing (FDB) engine and can be annoyingly loud at its maximum speed of 2200 RPM, though we expect it to almost never reach those speeds under normal operating conditions.

A trained eye will easily identify the OEM behind the NZXT C650 to be Seasonic, as it is based on a popular and highly decorated platform. NZXT did tweak the core platform a little to ensure compatibility with last-gen GPUs, but most of the reference design remains untouched. The heatsinks are relatively small and simplistic, suggesting (before testing) that the platform is either highly efficient or very loud.

The filtering stage begins on a small PCB at the back of the AC cable receptacle and continues on the main PCB. It is a reference design that consists of four Y capacitors, two X capacitors, two filtering inductors, and a surge-suppressing MOV. There are two bridge rectifiers sharing a single heatsink, which is uncommon for a unit with such a modest power output. The primary APFC capacitor is a 400V/470μF electrolytic capacitor made by Hitachi and is supported by a sizable coil.

Moving on to the primary inversion stage, we can see four transistors forming a typical full-bridge topology. Very few manufacturers opt for a full bridge design due to its cost, even with platforms designed for top-tier PSUs, yet it is more reliable and efficient than equivalent half-bridge topologies. They are mounted on small heatsinks in pairs, hinting the very high efficiency of both the topology and the transistors themselves.

The secondary side conversion stage is also simplistic, with just a couple of MOSFETs generating a single 12V line. The rest of the voltage lines are being generated by DC to DC converters that are mounted on a secondary daughterboard. All of the secondary capacitors, electrolytic and polymer alike, are supplied by Nippon Chemi-Con and Rubycon, making the C650 an all-Japanese affair.

Cold Test Results

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M  40 MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs - 2014 Pipeline post.

From the above charts, we can see that the NZXT C650 meets the 80Plus Gold certification requirements when powered from either a 230 VAC or 115 VAC outlet, even if only barely. It almost missed the certification requirements at 20% load and we can see that the efficiency of the PSU plummets as the load decreases, dropping well below 70% when the load is lower than 35 Watts. When the load drops below 20%, the efficiency drops so much that the raw power losses increase – a very rare effect. Apparently, this platform is not designed to cope with loads much lower than those intended.

We tested the NZXT C650 with its hybrid fan mode disabled, meaning that the fan was running at all times. In that scenario, the fan only became noticeable when the load ws greater than 320 Watts, and remained barely audible for loads up to 450 Watts. It eventually reached 42.9 dB(A) under maximum load, a passable noise figure for most users, and a great result from a PSU that is using a 120 mm fan. Considering that a PSU should never run at maximum load for prolonged periods of time, the NZXT C650 should be unnoticeable if installed inside a well-ventilated case.

Hot Test Results

As we can see in the following tables, the NZXT C650 delivers great power quality. The maximum voltage ripple on the 12V line is 28 mV, an unimpressive figure nowadays, but less than a quarter of the ATX design guide's recommended 120 mV limit. Ripple on the secondary 3.3V/5V lines is considerably worse, reaching 28 mV on the 5V line with a recommended maximum at 50 mV. We can notice the same pattern on voltage regulation, with the 12V line very tightly regulated at 0.7% and the regulation on the secondary 3.3V/5V lines reaching slightly over 2%.

Operation in high ambient temperatures does not affect the performance of the NZXT C650 considerably, regardless of the load. The average nominal load range (20%-100%) efficiency drops by 0.8% regardless of the input voltage, going down to an average of 89.8% (230 VAC) / 88.1% (115 VAC). There is very little change across the entire load range, suggesting that the components of the PSU are practically unaffected by the high ambient temperature. The component temperatures are high but not overly so.

As expected, the thermal control circuitry of the NZXT C650 correctly detects the high ambient temperature inside our hotbox and adjusts the fan’s speed accordingly. The NZXT C650 is not silent under these operating conditions, with the fan’s speed gradually increasing along with the load. Nevertheless, the sound pressure level tops out at just 50.2 dB(A), a figure significantly lower than what we would expect from a unit with a powerful 120 mm fan.

Conclusion

NZXT designed the C650 to land in the sweet spot of price and performance – offering excellent performance while remaining competitively priced – with an eye towards enticing enthusiasts who want to purchase an advanced PSU without breaking the bank. It's a great spot for buyers, but for manufacturers it can be a difficult one to compete in, especially with the prices of more advanced PSUs dropping with each passing day.

With its all-black chassis and cables, the NZXT C650 is an aesthetically neutral product, designed to subtly match the interior of any modern PC system. It features no lighting, which is a good thing for users that want to actually prevent the PSU from becoming the center of attention. Although NZXT is a company that enjoys making visually extravagant products, it seems that they preferred to keep the attitude - and cost - down on this one.

Quality is the strongest selling point of the NZXT C650. It is a unit based on a platform from Seasonic, arguably the most reputable PC PSU OEM, and it also happens to be a platform that was originally developed with long-term reliability in mind. The platform is designed so as to be efficient with the least possible stress on its parts, while the parts are all top quality products supplied by highly reputable manufacturers. It is no wonder why NZXT backs this unit up with a 10-year warranty – it is a product that, above all else, is designed to last.

The performance of the NZXT C650 is very good overall, with the designer clearly focusing on the power quality of the 12V line given the excellent figures we measured from the 12V rail. Readings from the 3.3V and 5V rails were not quite as good, though this isn't unique to NZXT, as most manufacturers tend to neglect the secondary voltage lines just a bit in favor of the major 12V line. The C650's thermal performance and acoustics were also well-balanced, creating a PSU that is quiet when expected and cool enough that it's not struggling to maintain that quiet nature.

As a result, the NZXT C650 is a great PSU overall, with NZXT making the right choice to focus on quality and longevity. The $110 price tag on the PSU is a little bold for an 80Plus Gold unit, and its current availability is rather limited – presumably due to COVID-released shipping backups – which is challenging the market potential of the product. Nonetheless, we feel that the very high quality and estimated longevity of the C650 will entice a significant portion of advanced users and enthusiasts, who enjoy purchasing products that will last them for many years to come.