I'm not familiar with Chartres. The Acoustic Revive review I found has a picture of the inside with a board that looks identical to the cheap China ones I bought for $10-12. The power supplies are so cheap they would seem a good candidate for power supply upgrades if one were interested in seeing how far they can go.
Acoustic Revive RR888 , Chartres mk. V and Chinese Schumann resonators.
I purchased Chartres mk.V Schumann resonator from Indonesia. The content of the box was somewhat disappointing. Second hand power supply, scratched and with some dirt. Open type casing makes it susceptible to dust. My friend owns AR RR-888 so.. we did some confrontation. We tested the devices at different locations (between the speakers, on side walls, behind the listening position) and at different heights (in the range of 5-7 feet). To make the long story short, we preferred the AR resonator by far. It's more effective, makes soundstage more expansive and images more saturated. Height close to 7 feet seems to be optimal. We used a cheap Chinese resonator (ZeroZone) for comparison as well. It worked somewhat but again, not even close to the AR.