Switching power supply design question

[torch]

Does the mains voltage and frequency affect the power output of a fixed voltage switching power supply with an input specification of 110 - 220VAC?

Specifically, I bought some from China specified to be 15W, but can only deliver 10W when supplied with 60Hz 117VAC. Before I complain, I want to make sure it's not possible that they can deliver 15W if supplied with 50Hz or 220VAC.

[jeroen79]

What happens when it draws 10W at 110V? Does it just shut down? Or does the voltage drop?
It would draw more current at 110V so perhaps that is the problem?

[ZeroStatic]

The power output of a 15W supply designed for 110-220VAC should be 15W regardless of supply voltage and frequency as long as it is within the specified range.

117VAC  is within the range specified.

You should complain.

[torch]

Above 10W, the voltage begins to sag, the product of VDC x A remaining about 10W.

11.8 * .88 = 10.4
10.2 * 1.01 = 10.3
7.36 * 1.28 = 9.42

 Rated current is 1.25 amps. Above 1.28 amps the unit shuts down.

As an experiment, I fed it through a variac that could supply up to 144VAC. The current available without voltage sag did increase slightly -- to 920 mA @12.2VDC or about 11W. I have no way to experiment with the frequency at mains voltage levels.

Note that I was using a pure resistive load (decade resistance box). The resistors are only rated 5W, so I was keeping it brief to avoid overheating. Nevertheless, there was some variation as they warmed up, so the numbers are approximate.

[Ian.M]

Input frequency wont make a lot of difference and a higher frequency may even be preferable if the design has insufficient reservoir capacitance on the primary side DC bus.

Remember: Chinese Wattage and Amparage ratings are like Sears horsepower, but generally more optimistic!

[T3sl4co1l]

Yup, it's poo.

Traditional ratings are inclusive, i.e., over X input range, Y output range will always be available.  There may be additional Y available for some values of X, but we don't care.

It seems likely that, in this case, they tested one combination and said "ship it".  As a result, you get a conditional range instead.

Tim