Need help on understanding something about UPS


I found an APC UPS unit (SMT750) that outputs:


And the PR4100’s power adapter outputs:
19 Volts
4.74 Amps
90 Watts

I’m kind of confused about this since this link shows that this UPS unit is supported, but isn’t the Amperage output of the UPS’s not enough for the PR4100?


Hello, SoftDisk

Well, you can have a look on the given article.

Technical Specifications

Output Power Capacity: 500 Watts / 750VA
Max Configurable Power: 500 Watts / 750VA
Nominal Output Voltage: 120V
Output Voltage Distortion: Less than 5% at full load
Output Frequency (sync to mains): 50/60Hz +/- 3Hz (auto sensing)
Topology: Line interactive
Waveform Type: Sine Wave
Output Connections: (6) NEMA 5-15R

The key spec:
Output Power Capacity: 500 Watts / 750VA
So, 500 Watts is more than enough to support the device because the My Cloud only needs 90 Watts which is less than the rated Watts.


Thanks for the reply, yeah i know about the required watts, but i always thought that the amperage is also very important, i read that if a power supply doesn’t output enough amperage to a device that it needs, that device might get damaged after a while.

so the APC unit looks like it outputs 4 amps (i think) and i’m not even sure if this is for each plug or the total of all, i have no idea how this really works.

And the PR4100 power adapter outputs 4.74 amps, so i’m guessing the NAS device needs more than 4 amps, am i correct?


The PR4100 power brick transforms high Voltage, low current to lower Voltage, high current.
At peak power usage, the PR4100 requires 19V (DC) x 4.7A, a peak of 90W at the output of the power brick.
That’s 220V x 0.7A x 0.7 (for AC) sourced at the input of the PR4100 power brick.

The UPC presented here is able to deliver 220V x 3.5A (AC) x 0.7 = 500W on its output, enough to power multiple PR4100 that require 90W at their peak power usage.

Simplified and probably a bit off calculations but I hope you get the picture.