Hmm the plot thickens for my old 360. I borrowed a different power supply, rated the same 203w, now my 360 flashes 3 red lights while the power supply goes to green and back to orange. (my old power supply simply went to red when trying to turn on the 360 with no reaction from the 360)
The Microsoft site is not very helpful, hardware problem with either 360 or power supply, thanks... If power supply goes green, 360 is kaput, goes red, power supply bad, stays orange try a different power socket. I tried a few, stays orange, 360 why you no like Canadian electricity :/
Any clue? Guess I'll bring it to my local shop to get advice what to do with it.
This is very similar to my brothers 360, and yes, its definitely our Canadian power, lol. JK.
It's a power problem, but not the new power brick most likely based on what your supply light is showing. Sounds like your old brick may have had a problem, or took a surge of some sort, which could have also affected the internal power circuit inside the console as well, since the console is older and now weak. Part of the power circuit for the 360 is inside the console itself. Thats where I had to replace my capacitors. I'm not saying its definitely your caps, beacuse there are a few things it could be within the power circuit, but its most likely in the console somewhere. I've read the mosfets in the power circuit shorting out are pretty common on certain 360's.
If you have no electrical knowledge, you could try and see visually if there's a problem, which could give you an idea where the problem lies. The problem isn't always clear to see visually though, so you could be wasting your time as well. You also would need to be a little careful because capacitors hold a charge and you could get shocked. It's unlikely, but possible if you don't know what your doing.
The mosfets will literally look burned or melted if it shows though visually, and the caps will either have the top "X" or "K" marking popped up like a dome instead of flat, or the bottom rubber is bulged out which usually leads to a tilted cap, or you will see some yellow fluid leaked out on top or below the cap. The cap can also be blown wide open on top with black "powder" all around it, but thats more rare.
If you can't visually see any of that, and don't have any electrical background, its best to take it in to a shop and have them use their equipment and knowledge to troubleshoot it.