Reddit mentions of 100-240V AC to 12V DC Power Supply with 4 Pin Molex (5A / 5000mA)

They use molex or sata power connectors.
If you want to test with your psu, make sure nothing else (motherboard, gpu, drive, ...) is connected and jump start your psu.
What I did last time was buy a 12V psu with molex connector and used that. Something like https://www.amazon.com/dp/B002TJNDU4

Couldn't you just use something like this and just make your life easy?

https://www.amazon.com/110v-Power-Supply-Molex-5000mA/dp/B002TJNDU4/ref=sr_1_1?ie=UTF8&qid=1481139320&sr=8-1&keywords=molex+to+ac+5a

This is what I have:

https://www.amazon.com/110v-Power-Supply-Molex-5000mA/dp/B002TJNDU4

If you're hellbent on it, they make external power for molex, then just molex to sata.

Here you go: http://www.amazon.com/110v-Power-Supply-Molex-5000mA/dp/B002TJNDU4

For the record, this is the power supply I used, and its been reliable: https://www.amazon.com/dp/B002TJNDU4

Okay, so the Walmart AC adapter is only 500mA. So that's not happening.

On amazon I found this 5A adapter and this 2A adapter.

Combined with this splitter, would these be a good solution? Is it possible to have too many amps and destroy the pump and fan?

You would need to pick up another HBA, with external SFF-8088 connectors on it, and hook it up to a JBOD enclosure.

Another option I've explored from time to time is something like this enclosure with breakout cables and a power supply.

The only reason I haven't jumped on the latter is because I don't fully trust the voltage regulation on that power supply (or any others I've found).