I found a Potion Bandoleer (Holds 6 pots and use them as minor act) in our game and had enough gold to buy 6 Power Jewels. Can I use this bandoleer with the Power Jewels? Is having more than one Power Jewel broken?
No, you cannot keep Power Jewels in the Potion Bandolier.
Well, you can, but the Potion Bandolier's property (drawing from it as a free action) only works for potions. Power Jewels are not potions. Storing them in the Potion Bandolier is thus no better than storing them anywhere else on your person, and probably worse if you have potions you could have put in the bandolier instead.
Having lots of Power Jewels is not broken or overpowered.
It can be strong if you have a particularly good level 1 or 3 encounter power, but generally speaking by the time you can afford a whole bunch of Power Jewels being able to refresh a level 1 or 3 encounter power isn't really much to get excited about.
It could be broken/overpowered if your DM ignores the parcel system and somehow lets you get a hold of a bunch of them at a lower level than would otherwise be possible, but hey, that's what happens when you tinker with the game's math, and frankly there are probably better uses of excessive loot/cash than Power Jewels.
There are two limits here.
Either A you respect item rarity rules, or B you respect daily item usage rules.
The potion bandoleer is completely pointless in this context, as the use of the jewel does not require you nomming it. It's just a minor action. (Assume it's sewn onto your clothing or something.)
In any event, spending 5k for:
Therefore, if you were allowed to purchase 5 of these somewhat cute things, (remember, powers must have a level to be used with this. Powers granted from class features that don't have a level don't count.) you wouldn't be able to use them because of daily item use limits.
Assuming your GM respects neither daily item use limits nor rarity rules (a huge mistake), you may certainly sew all 5 into your clothes and activate them without need for a potion bandoleer.
You also shouldn't need them. You have enough cash for a level 9 item. That means you should have 2-3 encounters already.