Your "reactor" is not more fuel or weight efficient than batteries or gasoline, but it is able to output massive surges of electrical output much like a miniaturized capacitor.
Capacitors are similar to batteries except the are able discharge MUCH faster. But they are also much bigger and heavier for how much they hold. So, instead of making a power source that outputs more total power, what you have is a device that can hold just as much electrical charge for its weight as a lithium ion battery, but can discharge it much faster when needed.
Current military prototypes for power armor have most of the bells and whistles you are asking for: heavy body armor, digitally enhanced optics, communications, etc. Because the power requirements of something the size of a person are so small, the average output of such a system during normal operation is only about about 30 watts.
Keep in mind that your power armor does not need a super powerful radar system onboard to see things 100km away, nor does a power suit have a lot of reasons to need to know what is 100km away since their main roles will be urban warfare and infiltration. They only need the ability to communicate with and integrate their tactical information with nearby vehicles or buildings that DO have longer sensory awareness. The power armor's sensory suite will be more interested in features like infrared, range finding, motion detectors, short range sonar, optical zoom, etc. which means your total electronics package's continuous power draw will likely be less than 10 watts.
Even climate control will not consume a lot of power. Since you are only air conditioning the narrow space between you and your suit by a few degrees, a the cooling system will use be orders of magnitude less power than something like a home AC or refrigerator. I would expect this to be about a 7 watt system, similar to the water cooling systems used on high end gaming PCs, but in normal climates, this power draw could be much less.
Walking/running around of course consumes more power, but this is something you will not be doing all day long on a normal mission. A solider spends a lot more time sitting and waiting than he does walking about; so, this could take an average of 10-13 watts even if the power use peaks much higher than this.
The only real power requirement of your suit that you do not already see in current power armor prototypes is the energy weapon(s). If the suit wants a HEL (High Energy Laser) capable of filling antipersonnel roles, it will need to output brief 2000 watt spikes of power. For one capable of taking on armored vehicles, it will need to spike up to 60,000-240,000 watts of power draw. These massive spikes of power discharge is what your system can do that modern batteries can not.
(This of course also assumes you've been able to massively improve laser technology to be able to make a hand held anti-tank laser to begin with.)
If you assume your power system is in every other way similar to the lithium ion batteries in current power armor prototypes, and you were to swap out the typical amount of ammo a solider carries with more batteries, then then your suit would have 72 hours of power set aside for normal field operation, plus an additional 130 hours of power for the extra batteries that are replacing your old ammo load out. With 130 hours of fuel "set aside as ammo" your power armor could in theory operate a 3 day mission, and fire enough shots to take out 65 main battle tanks, 260 light armored vehicles, or 7800 anti-personnel shots with its lasers... or the more likely scenario, allow the solider to operate an entire week between recharging and still be able to fire off the same amount of shots as a solider using bullets.
You could see the same tech used in other places, but it's effect would be far less noticeable.
In contrast, a Main Battle Tank like the M1 Abram consumes ~83 gallons of gasoline per hour. Replacing its engine with batteries would require a ~2,800,000 watt system. So, for a tank to also fire a 240,000 watt blast to kill another tank with a laser would not be nearly as extraordinary of a feat compared to what its existing power and weapon systems could already achieve. Furthermore, tanks do most of their killing with over the horizon weapons; so, replacing a tank's main gun with a direct fire energy weapon that needs line-of-sight would be at a strategical disadvantage against kinetic weapons anyway.
Aircraft consume even far more fuel than tanks. An F-22 for example can consume over 6000 gallons of fuel per hour. Also, aircraft rely a lot more on stealth, and it is a lot easier to fire a stealth missile from a stealth aircraft without being noticed than it is to fire a HEL which would light you up on infrared scanners.
So long story short, tanks and jets would still need their traditional engines and weapons because the power density of a lithium ion battery like system would be WAY to low to replace their primary propulsion systems and still maintain acceptable operational ranges, and the cost/benefit of directed energy weapons is not nearly as enticing for them as they are for infantry.