My Oppo is a bit too bright

Not sure I’d spend a lot on a 105D such as power supply or the IEC socket but no doubt it will help. I’d recommend using your Oppo as a transport and get a DAC. I have an Oppo 205 and it’s not up to my Cambridge 851C which I was using the DAC in it for my Bluesound Vault 2. I ended up getting a RME ADI 2fs DAC and it is better yet, much better and before I upgraded the power supply on the RME. 

If you’re using your Oppo for two channel only you can probably get enough out of it to pick up better dedicated CD player only like a used Cambridge 851C, or upper used Marantz models. If budget allows keep your Oppo and pick up a DAC.

tweak1

I totally agree it all starts with the PS, and don’t at all question the IEC socket didn’t help things but I think I’d still look at a DAC instead of putting the money into an Oppo first. That being said it still might makes sense to upgrade the Oppo as a transport only if one chooses another DAC. I’ve modified equipment myself and always achieved better sound but I don’t think a power supply alone will make an Oppo sound like say a RME DAC or others, but maybe it will. I’ve not heard a modified ModWright/Oppo player but owning a ModWright preamp I have no doubt Dan doesn’t transform the Oppo’s but at a much steeper price. I’ve thought about changing out the PS in my UDP-205, so maybe I’ll try it and report back... If for anything I can change out the fuse then.