Given your HP system, you probably don't have the OPTION of a power supply upgrade - you might have to settle for a RX 460 (which is somewhat of an upgrade but not a BIG one from the R9 270) to stay within the PS limits.
If you want to future-proof your system, avoid buying the "name brands" in the future, as they have a bad habit of building with "just enough" power supply to support the options THEY make available for the system.
