Archos Gmini220 Power Supply?

What does a power adapter do?
An AC adapter, AC/DC adapter, or AC/DC converter is a type of external power supply, often enclosed in a case similar to an AC plug. ... AC adapters are used with electrical devices that require power but do not contain internal components to derive the required voltage and power from mains power.
OR
power adapter. A power supply for electronic devices. Also called an "AC adapter" or "charger," power adapters plug into a wall outlet and convert AC to a single DC voltage. Computers use multiple DC voltages, and the power adapter is the external part of the power supply for a laptop.
https://www.pcmag.com/encyclopedia/term/power-adapter

Huawei OSN3500 doesn't have AC power supply,it power interface unit PIU is DC -48V input only, if you need a AC/DC power converter, I recommend ETP4890.

In fact, Huawei S6720 Switch has with 600W AC power supply, 350W DC power supply.
You can check in http://itprice.com/

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I'm not clear on the four pins of the DC power supply for the speakers. Do you think there two different voltages needed??? It's not worth trying to convert your ac power supply/ It would take a few parts and you will not end up with 18 vdc. You can purchase a 18 v dc adapter for as little as 15.00.

Check the DC supply from AC supply or try to replace the AC DC power your Netgear

short green and black

No.
AC power is like a child's swing -- it goes from "neutral" to "positive" to "neutral" to "negative" to "neutral", and repeats.
DC power is like leaning into a strong wind -- as long as you keep leaning, you stay on your feet; stop leaning, and the force of the wind will blow you down.

So, you cannot substitute AC for DC power.

I have a pair of Media 3 JBL computer speakers. I am using a generic 12V DC adapter rated at 1000mA with a positive tip polarity, and it works fine.

DC applied to any standard refrigerator would quickly damage the compressor motor and any fans present since these are all AC only motors.
Some (probably no longer produced) units used DC in their operation; - Peltier Efffect units that used a semiconductor device that acts as a 'heat pump,' removing heat from inside the cabinet and dissipating it outside. - A new type of compressor that hummed like a low frequency speaker and surely used DC in the generation of the driving signal.
The first proved to be less efficient than our near century old compressor system and the odd low frequency noise produced by the second could not be contained adequately for home use.