Efficiency

Using the efficiency results from the previous page, we plotted a chart which shows the SS-1250XM2's efficiency at low loads and loads equal to 20% -100% of the PSU's maximum-rated load.



Strangely enough, Seasonic's Gold-certified version of the platform clearly outperformed the Platinum unit at low loads, while the latter took the lead with normal loads, though only by a small margin. This unit's efficiency easily meets several Platinum platforms eye-to-eye, including the top-notch Leadex one, although the latter had an edge here because of its lower capacity.

Efficiency at Low Loads

In the next tests, we measured the efficiency of the SS-1250XM2 at loads much lower than 20% of its maximum-rated load (the lowest load the 80 Plus Standard measures). The loads we dialed were 40 W, 60 W, 80 W, and 100 W (for PSUs with over 500 W of capacity). This is important for settings where the PC is in idle mode with Power Saving turned on.


The PSU performed incredibly well at low loads as its efficiency scores were pretty high during even the 40 W load test. We should stress that high-wattage units usually don't register good efficiency at such low loads since—to put it as simply as possible—they use and need larger components (e.g. more caps of high capacity and larger coils), which lead to larger energy losses, and low-load tests are clearly more indicative of these losses than high-load tests.

5VSB Efficiency

The ATX specification states that 5VSB standby supply efficiency should be as high as possible and recommends 50% or higher efficiency with 100 mA of load, 60% or higher with 250 mA of load, and 70% or higher with 1 A or more of load.

We will take four measurements: one at 100, 250, and 1000 mA, each, and one with the full load the 5VSB rail can handle.


The 5VSB rail performed well and managed to crack the for this rail hard 80% mark.

Power Consumption in Idle & Standby

In the table below, you will find the power consumption and the voltage values of all rails (except -12V) when the PSU is in idle mode (powered on but without any load on its rails) and the power consumption when the PSU is in standby mode (without any load at 5VSB).


Typical for a modern PSU, the SS-1250XM2 consumes very little energy in idle.

Fan RPM, Delta Temperature & Output Noise

The cooling fan's speed (RPMs) and the delta difference between input and output temperature are illustrated in the following chart. The following results were obtained at 38°C-47°C ambient.



A chart that shows the cooling fan's speed (RPMs) and the output noise follows. We measure the fan's noise from 1 meter away, inside a small custom-made anechoic chamber whose internals are completely covered in specialized soundproofing material (Be Quiet! Noise Absorber Kit). Background noise inside the anechoic chamber was below 20 dBA during testing, and the results were obtained while the PSU operated at 38°C-47°C ambient.



The following graph illustrates the fan's output noise throughout the PSU's entire operating range. The same conditions as in the above graph applied to our measurements, but the ambient temperature was in-between 28°C and 30°C.



The unit's passive operation didn't last long, and output noise increased dramatically once the fan spun up. Its noise output with high loads will annoy most, and its noise output with mid-level loads can't be called quiet either.