**** Update 12 July 2016 ****
After hearing some reports of poor performance from the Genesis 2 adapter we recommended, I decided to purchase another one to make sure there was no manufacturing inconsistencies. What arrived was not the same as I previously tested. Turns out that Amazon sells a completely different Tomee product now in different packaging, which contradicts the photo on their product page. This new one is of awful design, and has circuitry similar to the 3-in-1 adapters we recommended avoiding entirely. I informed Amazon via telephone and they said they would review updating the listing to differentiate between the two. I updated the link in our post to point to another supply that we verified previously and is also affordable. Apologies to everyone who purchased this "revised" version without knowing it.
This was originally from a Kickstarter update, adapted for this website:
Something we have had our eye on for a while now is the use of new 3rd party power supplies (aka AC adapters, transformers, etc.) when powering Super Nintendos, Sega Master Systems, and Sega Genesis's. We have noticed that when using high quality component video, such as RGB or YPbPr, the power supply is a very important factor in determining the final picture quality. Poorly designed power supplies can introduce visible noise into the video outputs. The interesting thing to note is that this noise, while visible when using YPbPr, might not always be present when using composite video due to differences in how the signals are processed between the two formats. As such, someone experiencing this issue after upgrading to our component cables from standard composite cables might immediately pin the blame on our product instead of the power adapter they are using. Therefore, we are bringing this to your attention ahead of time.
We have tried and tested several different models of affordable 3rd party adapters. Not only did we verify that the video was free of noise, but Ste also disassembled each unit to confirm that the electrical and mechanical engineering of the adapter was solid and didn't have any safety concerns. We want to avoid recommending something that performs well, but is not safe on the inside.
As of right now, these are the most affordable 3rd party power adapters we currently recommend for use:
Sega Genesis 2 / Sega Genesis 3 / Sega Nomad / Sega 32X (UPDATED: 12 July 2016)
Super Nintendo (NOTE: Make sure part# is 7-38012-14010-9 and matches photo below)
Also, for multi-console setups, although it costs more money and isn't as available, we recommend the RetroDC.
We also want to highlight the adapters that you should stay away from. These two units are 3-in-1 universal supplies which are the most common and are carried in many local video game shops too. In fact, when selling you a console, they might bundle one of these along with it. It's our recommendation that you try asking them to leave the adapter out of the package and have them discount the console instead. Then you can use that saved money to buy a decent power adapter on your own. The only thing these units are good for are salvaging the SNES DC connector and splicing it onto a good power supply.
One last thing to mention is that this analysis only applies to new 3rd party AC adapters that can be easily found and purchased these days. The official Nintendo and Sega adapters that shipped with your consoles are perfectly fine and have no issues. We will also post more recommended power supply options as we discover them.