M, I'm sure some will say that these are the most-important caps in the amp. I don't agree totally with that, but conrad-johnson seems to believe it--some of their preamps use only film caps instead of electrolytics (els) in the PS. I can remember decades ago when the M75 (?) was upgraded to the M75a; they simply removed els from a decoupling position. I suppose that because the output transistors in a solidstate poweramp are connected directly to the last PS cap, the quality of the caps is MOST important.
I'd look at Michael Percy's el caps, here http://www.percyaudio.com/Catalog.pdf. See what you can afford, and don't forget that you can distribute the PS caps in different places around the amp and that it helps to use smaller values the closer to the output device the power gets. Also, I'd use as much polypropelene capacitance (the Solens are good choices here, as they're good quality, relatively 'small', and relatively inexpensive) as bypasses, with smaller, higher-quality bypasses (TRTs? MultiCap RTXs?), some as close to the transistors as I could get them.
I'd look at Michael Percy's el caps, here http://www.percyaudio.com/Catalog.pdf. See what you can afford, and don't forget that you can distribute the PS caps in different places around the amp and that it helps to use smaller values the closer to the output device the power gets. Also, I'd use as much polypropelene capacitance (the Solens are good choices here, as they're good quality, relatively 'small', and relatively inexpensive) as bypasses, with smaller, higher-quality bypasses (TRTs? MultiCap RTXs?), some as close to the transistors as I could get them.