There's more to power supply requirements than just the wattage. Basically you need to make sure your power supply puts out sufficient amps on the +12V rail(s) for the GPU. It also depends on the quality of the PSU they put in that... a lot of cheapo power supplies cannot actually provide the power they stated continuously, and do not have important things such as over current protection, or efficient power delivery at all loads (some buckle at certain loads).
Moreover, the Acer TC 105 from what I can see online has an AMD A8/A10 as the processor. This CPU is not powerful enough to support the Radeon R9 290X and getting this video card would be a colossal waste of money when stuck with an entry-level CPU.
Are you using an aftermarket power supply in your desktop? Because on the specifications I've found online for the Acer TC 105 show 300W power supply.
If you do not want to do a full upgrade, a GTX 750 Ti is a decent video card that shouldn't be held back by the A8/A10 processor, and has such a low power draw it'll work on almost any power supply.
Otherwise, your best bet would be to do a CPU, motherboard and GPU (and possibly power supply, depending on yours) upgrade. For $600 you could get a decent upgrade, that's plenty for an FX-6300, 970 motherboard, and a GTX 760/R9 280 and a good quality power supply. A bit of a hassle, but a GTX 760 or R9 280 will be delivering great performance for years to come.