I second the hum buster suggestion. There’s also a DIY DC blocker circuit I remember being mentioned here before. If you were into DIY, you could probably assemble it and basically make a Humbuster-like device yourself. These are likely your cheapest options to deal with DC if you can’t discover and eliminate the source of the DC.
Another alternative is to buy an isolation transformer unit, and plug your amps into that. Transformers block DC by their very nature. In fact, that is a key purpose of having them in your amps at all, to make sure only AC passes into the power supply circuits of the amp. But if you go the route of buying an isolation transformer unit, then you run the risk of the isolation transformer humming instead of your amps, depending on how sensitive it is to DC. I actually suspect I have DC in my line. I tried a relatively inexpensive non-audiophile type isolation transformer before, and it hummed like a beast. Unusable. Then I bought an Equi=Core brand balanced power transformer, and it only has a very light hum you can only hear when up close to the unit. Good enough for me. My whole system is plugged into it.
A balanced power transformer also has power conditioning benefits. By its very nature, it rejects a significant amount of noise on the AC. The Equi=Core product is the most affordable BPT I have seen on the market, and is only about half the cost of the PS Audio P5/P12 mentioned above. But significantly more expensive than the Humbuster approach.
And again, none of these will provide surge protection.
