The highest power to weight ratio electric or combustion engines could be used to power the Sarcos exoskeleton [as well as enable radically more efficient planes, cars, motorcycles and scooters].
The Sarcos exoskeleton just needs a good powersource and engine to power the hydraulics for it to enhance the strength and endurance of someone who wears it by ten times
It should be possible for someone with the untethered Sarcos exoskeleton to carry and use a minigun A M134 7.62 minigun weighs 190 lbs (60 pounds for the gun and 130 lbs for 1500 rounds of ammo)
The gun used in Terminator 2, Matrix (mounted on helicopter) and other movies. In real life used in Vietnam for firing out of helicopters.
The XM312 50 caliber gun could also be carried and used by one soldier in exoskeleton armor It delivers lethal and suppressive fire out to 2,000 meters.
New electric and combustion engines could be up to the task. It may be necessary to make half size versions of these engines to reduce the overall weight. The person wearing the exoskeleton can carry 100-200kg without tiring so having 60-100kg of weight for the power supply is doable.
The electric engine could be recharged with a solar cell tent or generators at a base camp. The gas engine could get refueled from Humvees or MRAPs or other vehicles.
Besides the weigh of engine the batteries of fuel weight needs to be considered.
A 13.2 kg, 30KW (40HP) electric engine made by Pipestrel
This electric engine is being used to make hyperfuel efficient motorized glider planes
Revetec,a small Australia company, has created an engine that is 50% smaller, 50% lighter, has 50% lower emissions and is cheaper to manufacture than a conventional internal combustion engine of the same horsepower. It doubles the fuel economy.
The X4v2 petrol engine achieved a repeatable Brake Specific Fuel Consumption (BSFC) figure of 212g/kW-h (38.6% engine efficiency) with a best figure of 207g/kW-h (39.5%) at our requested target test of 2,000rpm with a BMEP load of 450kpa (approximately 75% load) and an air/fuel ratio of 15.2:1 using 98 RON petrol and a 10:1 compression ratio. We also achieved a BSFC figure under the same rev and load conditions using an air/fuel ratio of 14.5:1 of 238g/kW-h (34.4%).
At 2000 rpm the engine generated 18kw and at higher rpm up to 65kw [24-87HP] The full load torque ranged from 132.9 to 176.1 Nm between 1500 and 3500 rpm.
The production engine weight for the X4V2 is 105 kg.
The engine for the killer Bee UAV only weighs 16 lbs and can get up to 25HP. Needs to be built with higher endurance as it needs overhaul every 300 hours.
Power to weight ratio
Projected advances in engine and power storage to 2020