Hello, so let's say I need a 15 watt power supply but that's all the information I have. The question is do I need a 3V/5A or a 5V/3A power supply and why is that information not included?

I won't post what device I need to power because what I want to know is why is it advertised as a 15w device, that's all. Thanks

 

You have a lot more options in your case. An infinite combination of (Voltage x Current) = 15. Take your pick.

How did you get 2 choices 3V/5A and 5V/3A? Or is it a blind choice?

If no further information is available, sorry, the help stops here. You need to let us know the Voltage of the device to be powered.

 

It may be a mains operated 15W device, so you won’t need a power supply at all,

 

It may be a mains operated 15W device, so you won’t need a power supply at all,

Then the voltage is known.

 

It sounds to me like you might be placing too much value on "advertising-hype".
Almost all of the pre-built Chinese stuff is extremely over-rated.
Very similar to Car-Audio Amps .......
"1500-WATTS" ....... but it has a 5-Amp Fuse and 22-ga. wiring !!!

If they don't provide hard maximum numbers, just move on.
.
.
.