Need help choosing a 3A 3.3V source

[zorobabel]

Hello good people!

First I want to mention that I know very little about electronics, I hope I can get some advice here.

I'm trying to fix an old Dell Powerconnect 2016 switch with a failed power supply. The power supply is a Delta 100-240V AC to 3.3V DC 3A; it is beyond my skill to fix it.
The board on the switch has 2 AME8815 Aecs250 regulators, which I believe put out 2.5V at 1.5A.
I've powered the switch for short periods of time and it works with power from a 5V 2.5A switching wallwart by itself, and with 1, 2 or 3 silicon diodes in series. My understanding of how the AME8815 works is less than basic, which brings me to the first question:
1. Will I fry the AME8815 regulators powering the board with the 5V 2.5A power supply? This regulator takes a maximum of 7V from looking at a spec sheet; I'm not sure if it has to dissipate some energy.

2. If the above is not an option, which of these cheap buck modules is more suited to the application? I can probably add some heatsinks. I can power them with 9, 12, 15 or 24V.
  2a. BenQ12v-5v-3.3v   More about it here: http://www.penguin.cz/~utx/hardware/Benq_LCD_power_supply/

http://www.ebay.com/itm/DC-DC-Buck-Converter-Step-Down-Voltage-LED-power-module-12V-switch-to-5V-3-3V-/141731613817?hash=item20ffdccc79:g:st0AAOSwAYtWIKRX&autorefresh=true

  2b. DC-DC XL4015      http://www.ebay.com/itm/DC-DC-XL4015-Step-Down-Adjustable-Power-Supply-Mod2ule-Lithium-Charger-5A-/262136733597?hash=item3d08911f9d:g:NQAAAOSwkZhWSYvw
 
  2c. MP1584EN            http://www.ebay.com/itm/1x-Mini-Adjustable-DC-DC-Converter-Step-down-Power-Supply-Module-3A-LM2596-L5RS-/381551378955?hash=item58d63c020b:g:7W8AAOSwezVWyd-6

From what I've been reading, heatsinks and toroid inductors are desirable for option 2b (LM2596).

Thanks for reading!

[michaeliv]

1. You will exceed the maximum power dissipation of the voltage regulators. They will likely overheat but not die immediately. You didn't specify the package for them (how they look like). They come in multiple packages. This defines the maximum power dissipation. Also you say you need 3A, not 2.5A, so that's another reason it won't work. Can you tell how they are wired ? are they simply in parallel ?
2. Option 2b is pretty good. I have that exact module and I tested it for ya ... at 5v it draws 2.7A to output 3.3A @ 3.3V. You probably won't even need a heatsink.

[zorobabel]

Thanks for the reply!
1. The package is TO-252. The die? is soldered to the board. The board is rather complicated, I can not tell if they are in series or parallel.
2. Thanks!

[michaeliv]

Each has a max power dissipation of 1.2W so let's say ideal scenario 2.4w. If you apply 5v directly the power dissipation would be 7.5W when fully loaded at 3A ... definitely more than is reasonable. So yes, go with the adjustable 2b.

[zorobabel]

Each has a max power dissipation of 1.2W so let's say ideal scenario 2.4w. If you apply 5v directly the power dissipation would be 7.5W when fully loaded at 3A ... definitely more than is reasonable. So yes, go with the adjustable 2b.

Thanks michaeliv, you've helped a lot!