There are a lot of them out there. Some are battery pack/Solar chargers (I suggest that type) The one I have depending on the level of sunlight can hit 6-7 Volts possibly more.... One device I have seems to "object" to this much charge.
Another option is a small (like 12 AH) LiFePo4 and a charge controller with a 100 watt panel (I have that too) Rather expensive but when the lights went out in my apartment.. the big inverter/battery pack kept the fridge cold and the little inverter/battery kept the freezer frozen (I have a small "Danfoss class" chest freezer) was very nice being able to keep things... cold.
Or I could use my Solar panel to charge a battery pack and use it to charge the other device.. in fact I think I'll try that.