Power Conditioner

I have Furman Elite 20PFI and like it very much.  I bought it used for about $650.  It has very tight non-sacrificial over/under voltage protection and I believe that it filters HF noise well.  My previous amp had plain unregulated power supply and did not suffer any loss of dynamics when plugged into it (high current bank).  I have whole house spike protection, but Furman already turned off circuit breaker few times.  When it happened I noticed bulbs got brighter for a moment.  Now with double protection I feel very safe.  Whole house protection is a must since everything these days is electronic, including appliances and even light bulbs, but Furman gives me extra protection for expensive gear.

The 20PFI has a big toroidal transformer inside to help with blocking A/C noise.  It also has the Power Factor Technology "current reservoir".  This is a big capacitor inside the power conditioner which gives faster immediate current to your devices which the A/C line would not normally provide.  The 20PFI is very expensive, but these two items really provide a lot more.

The 15PFI also has the "current reservoir" capacitor, but lacks the toroidal transformer.  It's less expensive, but still better than the "DMI".

Yes of course you need both. And don't forget the Orange Fuse.