Looks like a Huge weapon works without penalty
Wield Oversize Weapon says you can treat a weapon as one size category smaller than it is. Thus, you can treat a Huge weapon as if it were Large.
Powerful Build says you can wield weapons one size category larger than yourself without penalty. Since a goliath is a Medium creature, that means a goliath may wield Large weapons without penalty.
Since Wield Oversize Weapon lets you treat the Huge weapon as Large, and Powerful Build lets you wield Large weapons without penalty, you may wield a Huge weapon without penalty.
It does appear that by preventing Wield Oversize Weapon from working with Monkey Grip, the authors were trying to prevent exactly this, which could be an argument for an intent that this shouldn’t work. But by the rules-as-written, that applies only to Monkey Grip, not Powerful Build.
Please note that a size category larger weapon tends to deal only ~1 more damage than its smaller counterpart. There are some exceptions, but it still tends to be small amounts of damage. You can often gain more damage more quickly through other uses of feats. Note also that the size of your weapon does not affect reach (well, larger weapons don’t; too-small weapons do), so you do not get extended reach this way, either.
As for gloves of enlarge weapon, those are a really poor idea. If you meant strongarm bracers, those explicitly do not stack with Powerful Build.
In One Specific Case, Yes...
A creature possessing the feat Monkey Grip wielding a one-handed weapon designed for a creature one size category larger than the wielder can wield that one-handed, inappropriately bigger weapon one-handed.
For most other creatures--like those without the feat Monkey Grip--, that one-handed weapon designed for a creature one size larger than the wielder must be wielded as a two-handed weapon.
...But, Otherwise, No
The feat Monkey Grip (Complete Warrior 103) says
You can use melee weapons one size category larger than you are with a −2 penalty on the attack roll, but the amount of effort it takes you to use the weapon does not change.
Thus if the weapon is not designed for creatures one size category larger than the creature that is attempting to employ the weapon, the feat Monkey Grip has no effect.
Example
Without the feat Monkey Grip a Medium creature attempting to wield a Large weapon...
- wields a Large light weapon as a one-handed weapon and suffers a -2 penalty to attack rolls.
- wields a Large one-handed weapon as a two-handed weapon and suffers a -2 penalty to attack rolls.
- can't wield a Large two-handed weapon at all.
With the feat Monkey Grip a Medium creature attempting to wield a Large weapon...
- wields a Large light weapon as a light weapon and suffers a -2 penalty to attack rolls.
- wields a Large one-handed weapon as a one-handed weapon and suffers a -2 penalty to attack rolls.
- wields a Large two-handed weapon as a two-handed weapon and suffers a -2 penalty to attack rolls.
With or without the feat Monkey Grip, a creature wields a two-handed weapon that is designed for a creature of its own size category as a two-handed weapon. Just because a creature can use something designed for bigger creatures easier doesn't mean the creature can use something designed for creatures of its own size even more easier.
When the feat says in its example...
[A] Large longsword (a one-handed weapon for a Large creature) is considered a two-handed weapon for a Medium creature that does not have this feat.
...the feat's trying to make clear that it's not referring to the actual size of the longsword. That was the case in Dungeons and Dragons, 3rd Edition (where a greatsword for a Medium creature was actually a longsword for Large creature), but the weapon size rules changed significantly between 3rd Edition and 3.5. In the example in the feat Monkey Grip, the Large in Large longsword refers to the size of the creature for which the weapon is designed rather than the weapon itself. Thus, no, for the purposes of this feat a two-handed Medium weapon and a Large one-handed weapon are not the same and shouldn't be treated the same for purposes of this feat.
Mathematically, it's really not a very good feat. For role-playing, though, it enables a creature to use a ridiculously big weapon, and that's worth it to some folks.
The Sage's Succinctness
The Dragon #357 Sage Advice column "Official Answers to Your Questions" (83-4) contains this exchange between a reader and then-sage Andy Collins:
If Monkey Grip (Complete Warrior, 103) can be used to wield a weapon one size category larger without extra effort, can you instead wield a two-handed weapon of your size category with one hand?
Technically no--the feat specifically applies to weapons one size category larger than you.
Best Answer
You don't need the feat in 5E to wield oversized weapons
The DMG section on creating a monster provides rules for using oversized weapons under "Step 11. Damage" (p. 278; emphasis mine):
Disadvantage is, on average, equivalent to -5 on the roll (dependent on what the total number required to hit is). You could justifiably create a homebrewed feat that improved this to a static -2 penalty instead of disadvantage, provided the DM approves (just in case you aren't the DM).